Analysis of join usage in MySQL
Analysis of join usage in MySQL
The example database is as follows:
student table:
mysql> select * from student; +-----------+-----------+------+------+-------+ | Sno | Sname | Ssex | Sage | Sdept | +-----------+-----------+------+------+-------+ | 201215121 | 李勇 | 男 | 22 | CS | | 201215122 | 刘晨 | 女 | 19 | CS | | 201215123 | 王敏 | 女 | 18 | MA | | 201215125 | 张立 | 男 | 19 | IS | | 201215128 | 陈冬 | 男 | 18 | IS | | 201215126 | 张成民 | 男 | 18 | CS | +-----------+-----------+------+------+-------+6 rows in set (0.00 sec)
sc Table:
mysql> select * from sc; +-----------+------+-------+ | Sno | Cno | Grade | +-----------+------+-------+ | 201215121 | 1 | 92 | | 201215121 | 2 | 85 | | 201215121 | 3 | 88 | | 201215122 | 2 | 90 | | 201215122 | 3 | 80 | | 201215128 | 1 | 78 | +-----------+------+-------+6 rows in set (0.00 sec)
LEFT JOIN (left join)
The sql statement is as follows:
select * from student left join sc on student.Sno=sc.Sno;
The running results are as follows:
+-----------+-----------+------+------+-------+-----------+------+-------+ | Sno | Sname | Ssex | Sage | Sdept | Sno | Cno | Grade | +-----------+-----------+------+------+-------+-----------+------+-------+ | 201215121 | 李勇 | 男 | 22 | CS | 201215121 | 1 | 92 | | 201215121 | 李勇 | 男 | 22 | CS | 201215121 | 2 | 85 | | 201215121 | 李勇 | 男 | 22 | CS | 201215121 | 3 | 88 | | 201215122 | 刘晨 | 女 | 19 | CS | 201215122 | 2 | 90 | | 201215122 | 刘晨 | 女 | 19 | CS | 201215122 | 3 | 80 | | 201215128 | 陈冬 | 男 | 18 | IS | 201215128 | 1 | 78 | | 201215123 | 王敏 | 女 | 18 | MA | NULL | NULL | NULL | | 201215125 | 张立 | 男 | 19 | IS | NULL | NULL | NULL | | 201215126 | 张成民 | 男 | 18 | CS | NULL | NULL | NULL | +-----------+-----------+------+------+-------+-----------+------+-------+
in In this example, the left join is based on the records in the student table. The student table can be regarded as the left table, and the sc table can be regarded as the right table. The records in the left table will be fully displayed, plus the matching right table. If If there is no match on the left side, the remaining parts will be displayed as null.
USING clause
The using clause and the on clause are similar, but the results are slightly different.
For example:
mysql> select student.Sno,Sname,Grade from student left join sc on student.Sno=sc.Sno; +-----------+-----------+-------+ | Sno | Sname | Grade | +-----------+-----------+-------+ | 201215121 | 李勇 | 92 | | 201215121 | 李勇 | 85 | | 201215121 | 李勇 | 88 | | 201215122 | 刘晨 | 90 | | 201215122 | 刘晨 | 80 | | 201215128 | 陈冬 | 78 | | 201215123 | 王敏 | NULL | | 201215125 | 张立 | NULL | | 201215126 | 张成民 | NULL | +-----------+-----------+-------+ 9 rows in set (0.00 sec)
The above is equivalent to
select Sno,Sname,Grade from student left join sc using(Sno); +-----------+-----------+-------+ | Sno | Sname | Grade | +-----------+-----------+-------+ | 201215121 | 李勇 | 92 | | 201215121 | 李勇 | 85 | | 201215121 | 李勇 | 88 | | 201215122 | 刘晨 | 90 | | 201215122 | 刘晨 | 80 | | 201215128 | 陈冬 | 78 | | 201215123 | 王敏 | NULL | | 201215125 | 张立 | NULL | | 201215126 | 张成民 | NULL | +-----------+-----------+-------+
in different places, for example:
select * from student left join sc on student.Sno=sc.Sno; +-----------+-----------+------+------+-------+-----------+------+-------+ | Sno | Sname | Ssex | Sage | Sdept | Sno | Cno | Grade | +-----------+-----------+------+------+-------+-----------+------+-------+ | 201215121 | 李勇 | 男 | 22 | CS | 201215121 | 1 | 92 | | 201215121 | 李勇 | 男 | 22 | CS | 201215121 | 2 | 85 | | 201215121 | 李勇 | 男 | 22 | CS | 201215121 | 3 | 88 | | 201215122 | 刘晨 | 女 | 19 | CS | 201215122 | 2 | 90 | | 201215122 | 刘晨 | 女 | 19 | CS | 201215122 | 3 | 80 | | 201215128 | 陈冬 | 男 | 18 | IS | 201215128 | 1 | 78 | | 201215123 | 王敏 | 女 | 18 | MA | NULL | NULL | NULL | | 201215125 | 张立 | 男 | 19 | IS | NULL | NULL | NULL | | 201215126 | 张成民 | 男 | 18 | CS | NULL | NULL | NULL | +-----------+-----------+------+------+-------+-----------+------+-------+
select * from student left join sc using (sno); +-----------+-----------+------+------+-------+------+-------+ | Sno | Sname | Ssex | Sage | Sdept | Cno | Grade | +-----------+-----------+------+------+-------+------+-------+ | 201215121 | 李勇 | 男 | 22 | CS | 1 | 92 | | 201215121 | 李勇 | 男 | 22 | CS | 2 | 85 | | 201215121 | 李勇 | 男 | 22 | CS | 3 | 88 | | 201215122 | 刘晨 | 女 | 19 | CS | 2 | 90 | | 201215122 | 刘晨 | 女 | 19 | CS | 3 | 80 | | 201215128 | 陈冬 | 男 | 18 | IS | 1 | 78 | | 201215123 | 王敏 | 女 | 18 | MA | NULL | NULL | | 201215125 | 张立 | 男 | 19 | IS | NULL | NULL | | 201215126 | 张成民 | 男 | 18 | CS | NULL | NULL | +-----------+-----------+------+------+-------+------+-------+
The repeated Sno column will be output twice if the on word is used.
RIGHT JOIN (right join)
Same as LEFT JOIN, but based on the right table, for example:
select * from student right join sc using (sno); +-----------+------+-------+--------+------+------+-------+ | Sno | Cno | Grade | Sname | Ssex | Sage | Sdept | +-----------+------+-------+--------+------+------+-------+ | 201215121 | 1 | 92 | 李勇 | 男 | 22 | CS | | 201215121 | 2 | 85 | 李勇 | 男 | 22 | CS | | 201215121 | 3 | 88 | 李勇 | 男 | 22 | CS | | 201215122 | 2 | 90 | 刘晨 | 女 | 19 | CS | | 201215122 | 3 | 80 | 刘晨 | 女 | 19 | CS | | 201215128 | 1 | 78 | 陈冬 | 男 | 18 | IS | +-----------+------+-------+--------+------+------+-------+
INNER JOIN (equal join or inner join)
It will not show who it is based on, only the records that meet the conditions will be displayed
select * from student inner join sc on student.Sno=sc.Sno; +-----------+--------+------+------+-------+-----------+------+-------+ | Sno | Sname | Ssex | Sage | Sdept | Sno | Cno | Grade | +-----------+--------+------+------+-------+-----------+------+-------+ | 201215121 | 李勇 | 男 | 22 | CS | 201215121 | 1 | 92 | | 201215121 | 李勇 | 男 | 22 | CS | 201215121 | 2 | 85 | | 201215121 | 李勇 | 男 | 22 | CS | 201215121 | 3 | 88 | | 201215122 | 刘晨 | 女 | 19 | CS | 201215122 | 2 | 90 | | 201215122 | 刘晨 | 女 | 19 | CS | 201215122 | 3 | 80 | | 201215128 | 陈冬 | 男 | 18 | IS | 201215128 | 1 | 78 | +-----------+--------+------+------+-------+-----------+------+-------+
The above statement is equivalent to:
select * from student,sc where student.Sno=sc.Sno; +-----------+--------+------+------+-------+-----------+------+-------+ | Sno | Sname | Ssex | Sage | Sdept | Sno | Cno | Grade | +-----------+--------+------+------+-------+-----------+------+-------+ | 201215121 | 李勇 | 男 | 22 | CS | 201215121 | 1 | 92 | | 201215121 | 李勇 | 男 | 22 | CS | 201215121 | 2 | 85 | | 201215121 | 李勇 | 男 | 22 | CS | 201215121 | 3 | 88 | | 201215122 | 刘晨 | 女 | 19 | CS | 201215122 | 2 | 90 | | 201215122 | 刘晨 | 女 | 19 | CS | 201215122 | 3 | 80 | | 201215128 | 陈冬 | 男 | 18 | IS | 201215128 | 1 | 78 | +-----------+--------+------+------+-------+-----------+------+-------+
Extension
If you only want to retrieve some records from table A, but do not include table B
You can add a where statement after the left join
select * from student left join sc using(Sno) where sc.Sno is null; +-----------+-----------+------+------+-------+------+-------+ | Sno | Sname | Ssex | Sage | Sdept | Cno | Grade | +-----------+-----------+------+------+-------+------+-------+ | 201215123 | 王敏 | 女 | 18 | MA | NULL | NULL | | 201215125 | 张立 | 男 | 19 | IS | NULL | NULL | | 201215126 | 张成民 | 男 | 18 | CS | NULL | NULL | +-----------+-----------+------+------+-------+------+-------+
Find the difference set
#You can combine union words. Since in this example, all the ones on the right are corresponding, so the displayed result is consistent with the previous one.
select * from student left join sc using(Sno) where student.Sno is null union select * from student left join sc using(Sno) where sc.Sno is null; +-----------+-----------+------+------+-------+------+-------+ | Sno | Sname | Ssex | Sage | Sdept | Cno | Grade | +-----------+-----------+------+------+-------+------+-------+ | 201215123 | 王敏 | 女 | 18 | MA | NULL | NULL | | 201215125 | 张立 | 男 | 19 | IS | NULL | NULL | | 201215126 | 张成民 | 男 | 18 | CS | NULL | NULL | +-----------+-----------+------+------+-------+------+-------+
FULL JOIN
select * from student left join sc on student.Sno=sc.Sno union select * from student right join sc on student.Sno=sc.Sno; +-----------+-----------+------+------+-------+-----------+------+-------+ | Sno | Sname | Ssex | Sage | Sdept | Sno | Cno | Grade | +-----------+-----------+------+------+-------+-----------+------+-------+ | 201215121 | 李勇 | 男 | 22 | CS | 201215121 | 1 | 92 | | 201215121 | 李勇 | 男 | 22 | CS | 201215121 | 2 | 85 | | 201215121 | 李勇 | 男 | 22 | CS | 201215121 | 3 | 88 | | 201215122 | 刘晨 | 女 | 19 | CS | 201215122 | 2 | 90 | | 201215122 | 刘晨 | 女 | 19 | CS | 201215122 | 3 | 80 | | 201215128 | 陈冬 | 男 | 18 | IS | 201215128 | 1 | 78 | | 201215123 | 王敏 | 女 | 18 | MA | NULL | NULL | NULL | | 201215125 | 张立 | 男 | 19 | IS | NULL | NULL | NULL | | 201215126 | 张成民 | 男 | 18 | CS | NULL | NULL | NULL | +-----------+-----------+------+------+-------+-----------+------+-------+
Note: A left join B is equivalent to B right join A
mysql> select * from student left join sc using(Sno); +-----------+-----------+------+------+-------+------+-------+ | Sno | Sname | Ssex | Sage | Sdept | Cno | Grade | +-----------+-----------+------+------+-------+------+-------+ | 201215121 | 李勇 | 男 | 22 | CS | 1 | 92 | | 201215121 | 李勇 | 男 | 22 | CS | 2 | 85 | | 201215121 | 李勇 | 男 | 22 | CS | 3 | 88 | | 201215122 | 刘晨 | 女 | 19 | CS | 2 | 90 | | 201215122 | 刘晨 | 女 | 19 | CS | 3 | 80 | | 201215128 | 陈冬 | 男 | 18 | IS | 1 | 78 | | 201215123 | 王敏 | 女 | 18 | MA | NULL | NULL | | 201215125 | 张立 | 男 | 19 | IS | NULL | NULL | | 201215126 | 张成民 | 男 | 18 | CS | NULL | NULL | +-----------+-----------+------+------+-------+------+-------+ 9 rows in set (0.00 sec)mysql> select * from sc right join student using(Sno); +-----------+-----------+------+------+-------+------+-------+ | Sno | Sname | Ssex | Sage | Sdept | Cno | Grade | +-----------+-----------+------+------+-------+------+-------+ | 201215121 | 李勇 | 男 | 22 | CS | 1 | 92 | | 201215121 | 李勇 | 男 | 22 | CS | 2 | 85 | | 201215121 | 李勇 | 男 | 22 | CS | 3 | 88 | | 201215122 | 刘晨 | 女 | 19 | CS | 2 | 90 | | 201215122 | 刘晨 | 女 | 19 | CS | 3 | 80 | | 201215128 | 陈冬 | 男 | 18 | IS | 1 | 78 | | 201215123 | 王敏 | 女 | 18 | MA | NULL | NULL | | 201215125 | 张立 | 男 | 19 | IS | NULL | NULL | | 201215126 | 张成民 | 男 | 18 | CS | NULL | NULL | +-----------+-----------+------+------+-------+------+-------+
Join usage analysis in MySQL
The instance database is as follows:
student table:
mysql> select * from student; +-----------+-----------+------+------+-------+ | Sno | Sname | Ssex | Sage | Sdept | +-----------+-----------+------+------+-------+ | 201215121 | 李勇 | 男 | 22 | CS | | 201215122 | 刘晨 | 女 | 19 | CS | | 201215123 | 王敏 | 女 | 18 | MA | | 201215125 | 张立 | 男 | 19 | IS | | 201215128 | 陈冬 | 男 | 18 | IS | | 201215126 | 张成民 | 男 | 18 | CS | +-----------+-----------+------+------+-------+ 6 rows in set (0.00 sec)
sc table:
mysql> select * from sc; +-----------+------+-------+ | Sno | Cno | Grade | +-----------+------+-------+ | 201215121 | 1 | 92 | | 201215121 | 2 | 85 | | 201215121 | 3 | 88 | | 201215122 | 2 | 90 | | 201215122 | 3 | 80 | | 201215128 | 1 | 78 | +-----------+------+-------+ 6 rows in set (0.00 sec)
LEFT JOIN (left join)
##sql The statement is as follows:
select * from student left join sc on student.Sno=sc.Sno;
+-----------+-----------+------+------+-------+-----------+------+-------+ | Sno | Sname | Ssex | Sage | Sdept | Sno | Cno | Grade | +-----------+-----------+------+------+-------+-----------+------+-------+ | 201215121 | 李勇 | 男 | 22 | CS | 201215121 | 1 | 92 | | 201215121 | 李勇 | 男 | 22 | CS | 201215121 | 2 | 85 | | 201215121 | 李勇 | 男 | 22 | CS | 201215121 | 3 | 88 | | 201215122 | 刘晨 | 女 | 19 | CS | 201215122 | 2 | 90 | | 201215122 | 刘晨 | 女 | 19 | CS | 201215122 | 3 | 80 | | 201215128 | 陈冬 | 男 | 18 | IS | 201215128 | 1 | 78 | | 201215123 | 王敏 | 女 | 18 | MA | NULL | NULL | NULL | | 201215125 | 张立 | 男 | 19 | IS | NULL | NULL | NULL | | 201215126 | 张成民 | 男 | 18 | CS | NULL | NULL | NULL | +-----------+-----------+------+------+-------+-----------+------+-------+
For example:
mysql> select student.Sno,Sname,Grade from student left join sc on student.Sno=sc.Sno; +-----------+-----------+-------+| Sno | Sname | Grade | +-----------+-----------+-------+| 201215121 | 李勇 | 92 | | 201215121 | 李勇 | 85 | | 201215121 | 李勇 | 88 | | 201215122 | 刘晨 | 90 | | 201215122 | 刘晨 | 80 | | 201215128 | 陈冬 | 78 | | 201215123 | 王敏 | NULL | | 201215125 | 张立 | NULL || 201215126 | 张成民 | NULL | +-----------+-----------+-------+9 rows in set (0.00 sec)
select Sno,Sname,Grade from student left join sc using(Sno); +-----------+-----------+-------+| Sno | Sname | Grade | +-----------+-----------+-------+| 201215121 | 李勇 | 92 | | 201215121 | 李勇 | 85 | | 201215121 | 李勇 | 88 | | 201215122 | 刘晨 | 90 | | 201215122 | 刘晨 | 80 | | 201215128 | 陈冬 | 78 | | 201215123 | 王敏 | NULL | | 201215125 | 张立 | NULL || 201215126 | 张成民 | NULL | +-----------+-----------+-------+
select * from student left join sc on student.Sno=sc.Sno; +-----------+-----------+------+------+-------+-----------+------+-------+ | Sno | Sname | Ssex | Sage | Sdept | Sno | Cno | Grade | +-----------+-----------+------+------+-------+-----------+------+-------+ | 201215121 | 李勇 | 男 | 22 | CS | 201215121 | 1 | 92 | | 201215121 | 李勇 | 男 | 22 | CS | 201215121 | 2 | 85 | | 201215121 | 李勇 | 男 | 22 | CS | 201215121 | 3 | 88 | | 201215122 | 刘晨 | 女 | 19 | CS | 201215122 | 2 | 90 | | 201215122 | 刘晨 | 女 | 19 | CS | 201215122 | 3 | 80 | | 201215128 | 陈冬 | 男 | 18 | IS | 201215128 | 1 | 78 | | 201215123 | 王敏 | 女 | 18 | MA | NULL | NULL | NULL | | 201215125 | 张立 | 男 | 19 | IS | NULL | NULL | NULL | | 201215126 | 张成民 | 男 | 18 | CS | NULL | NULL | NULL | +-----------+-----------+------+------+-------+-----------+------+-------+
select * from student left join sc using (sno); +-----------+-----------+------+------+-------+------+-------+ | Sno | Sname | Ssex | Sage | Sdept | Cno | Grade | +-----------+-----------+------+------+-------+------+-------+ | 201215121 | 李勇 | 男 | 22 | CS | 1 | 92 | | 201215121 | 李勇 | 男 | 22 | CS | 2 | 85 | | 201215121 | 李勇 | 男 | 22 | CS | 3 | 88 | | 201215122 | 刘晨 | 女 | 19 | CS | 2 | 90 | | 201215122 | 刘晨 | 女 | 19 | CS | 3 | 80 | | 201215128 | 陈冬 | 男 | 18 | IS | 1 | 78 | | 201215123 | 王敏 | 女 | 18 | MA | NULL | NULL | | 201215125 | 张立 | 男 | 19 | IS | NULL | NULL | | 201215126 | 张成民 | 男 | 18 | CS | NULL | NULL | +-----------+-----------+------+------+-------+------+-------+
select * from student right join sc using (sno); +-----------+------+-------+--------+------+------+-------+ | Sno | Cno | Grade | Sname | Ssex | Sage | Sdept | +-----------+------+-------+--------+------+------+-------+ | 201215121 | 1 | 92 | 李勇 | 男 | 22 | CS | | 201215121 | 2 | 85 | 李勇 | 男 | 22 | CS | | 201215121 | 3 | 88 | 李勇 | 男 | 22 | CS | | 201215122 | 2 | 90 | 刘晨 | 女 | 19 | CS | | 201215122 | 3 | 80 | 刘晨 | 女 | 19 | CS | | 201215128 | 1 | 78 | 陈冬 | 男 | 18 | IS | +-----------+------+-------+--------+------+------+-------+
select * from student inner join sc on student.Sno=sc.Sno; +-----------+--------+------+------+-------+-----------+------+-------+ | Sno | Sname | Ssex | Sage | Sdept | Sno | Cno | Grade | +-----------+--------+------+------+-------+-----------+------+-------+ | 201215121 | 李勇 | 男 | 22 | CS | 201215121 | 1 | 92 | | 201215121 | 李勇 | 男 | 22 | CS | 201215121 | 2 | 85 | | 201215121 | 李勇 | 男 | 22 | CS | 201215121 | 3 | 88 | | 201215122 | 刘晨 | 女 | 19 | CS | 201215122 | 2 | 90 | | 201215122 | 刘晨 | 女 | 19 | CS | 201215122 | 3 | 80 | | 201215128 | 陈冬 | 男 | 18 | IS | 201215128 | 1 | 78 | +-----------+--------+------+------+-------+-----------+------+-------+
select * from student,sc where student.Sno=sc.Sno; +-----------+--------+------+------+-------+-----------+------+-------+ | Sno | Sname | Ssex | Sage | Sdept | Sno | Cno | Grade | +-----------+--------+------+------+-------+-----------+------+-------+ | 201215121 | 李勇 | 男 | 22 | CS | 201215121 | 1 | 92 | | 201215121 | 李勇 | 男 | 22 | CS | 201215121 | 2 | 85 | | 201215121 | 李勇 | 男 | 22 | CS | 201215121 | 3 | 88 | | 201215122 | 刘晨 | 女 | 19 | CS | 201215122 | 2 | 90 | | 201215122 | 刘晨 | 女 | 19 | CS | 201215122 | 3 | 80 | | 201215128 | 陈冬 | 男 | 18 | IS | 201215128 | 1 | 78 | +-----------+--------+------+------+-------+-----------+------+-------+
select * from student left join sc using(Sno) where sc.Sno is null; +-----------+-----------+------+------+-------+------+-------+ | Sno | Sname | Ssex | Sage | Sdept | Cno | Grade | +-----------+-----------+------+------+-------+------+-------+ | 201215123 | 王敏 | 女 | 18 | MA | NULL | NULL | | 201215125 | 张立 | 男 | 19 | IS | NULL | NULL | | 201215126 | 张成民 | 男 | 18 | CS | NULL | NULL | +-----------+-----------+------+------+-------+------+-------+
select * from student left join sc using(Sno) where student.Sno is null union select * from student left join sc using(Sno) where sc.Sno is null; +-----------+-----------+------+------+-------+------+-------+ | Sno | Sname | Ssex | Sage | Sdept | Cno | Grade | +-----------+-----------+------+------+-------+------+-------+ | 201215123 | 王敏 | 女 | 18 | MA | NULL | NULL | | 201215125 | 张立 | 男 | 19 | IS | NULL | NULL | | 201215126 | 张成民 | 男 | 18 | CS | NULL | NULL | +-----------+-----------+------+------+-------+------+-------+
select * from student left join sc on student.Sno=sc.Sno union select * from student right join sc on student.Sno=sc.Sno; +-----------+-----------+------+------+-------+-----------+------+-------+ | Sno | Sname | Ssex | Sage | Sdept | Sno | Cno | Grade | +-----------+-----------+------+------+-------+-----------+------+-------+ | 201215121 | 李勇 | 男 | 22 | CS | 201215121 | 1 | 92 | | 201215121 | 李勇 | 男 | 22 | CS | 201215121 | 2 | 85 | | 201215121 | 李勇 | 男 | 22 | CS | 201215121 | 3 | 88 | | 201215122 | 刘晨 | 女 | 19 | CS | 201215122 | 2 | 90 | | 201215122 | 刘晨 | 女 | 19 | CS | 201215122 | 3 | 80 | | 201215128 | 陈冬 | 男 | 18 | IS | 201215128 | 1 | 78 | | 201215123 | 王敏 | 女 | 18 | MA | NULL | NULL | NULL | | 201215125 | 张立 | 男 | 19 | IS | NULL | NULL | NULL | | 201215126 | 张成民 | 男 | 18 | CS | NULL | NULL | NULL | +-----------+-----------+------+------+-------+-----------+------+-------+
mysql> select * from student left join sc using(Sno); +-----------+-----------+------+------+-------+------+-------+ | Sno | Sname | Ssex | Sage | Sdept | Cno | Grade | +-----------+-----------+------+------+-------+------+-------+ | 201215121 | 李勇 | 男 | 22 | CS | 1 | 92 | | 201215121 | 李勇 | 男 | 22 | CS | 2 | 85 | | 201215121 | 李勇 | 男 | 22 | CS | 3 | 88 | | 201215122 | 刘晨 | 女 | 19 | CS | 2 | 90 | | 201215122 | 刘晨 | 女 | 19 | CS | 3 | 80 | | 201215128 | 陈冬 | 男 | 18 | IS | 1 | 78 | | 201215123 | 王敏 | 女 | 18 | MA | NULL | NULL | | 201215125 | 张立 | 男 | 19 | IS | NULL | NULL | | 201215126 | 张成民 | 男 | 18 | CS | NULL | NULL | +-----------+-----------+------+------+-------+------+-------+ 9 rows in set (0.00 sec)mysql> select * from sc right join student using(Sno); +-----------+-----------+------+------+-------+------+-------+ | Sno | Sname | Ssex | Sage | Sdept | Cno | Grade | +-----------+-----------+------+------+-------+------+-------+ | 201215121 | 李勇 | 男 | 22 | CS | 1 | 92 | | 201215121 | 李勇 | 男 | 22 | CS | 2 | 85 | | 201215121 | 李勇 | 男 | 22 | CS | 3 | 88 | | 201215122 | 刘晨 | 女 | 19 | CS | 2 | 90 | | 201215122 | 刘晨 | 女 | 19 | CS | 3 | 80 | | 201215128 | 陈冬 | 男 | 18 | IS | 1 | 78 | | 201215123 | 王敏 | 女 | 18 | MA | NULL | NULL | | 201215125 | 张立 | 男 | 19 | IS | NULL | NULL | | 201215126 | 张成民 | 男 | 18 | CS | NULL | NULL | +-----------+-----------+------+------+-------+------+-------+
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MySQL is chosen for its performance, reliability, ease of use, and community support. 1.MySQL provides efficient data storage and retrieval functions, supporting multiple data types and advanced query operations. 2. Adopt client-server architecture and multiple storage engines to support transaction and query optimization. 3. Easy to use, supports a variety of operating systems and programming languages. 4. Have strong community support and provide rich resources and solutions.
How to start mysql by docker
Apr 15, 2025 pm 12:09 PM
The process of starting MySQL in Docker consists of the following steps: Pull the MySQL image to create and start the container, set the root user password, and map the port verification connection Create the database and the user grants all permissions to the database
MySQL's Role: Databases in Web Applications
Apr 17, 2025 am 12:23 AM
The main role of MySQL in web applications is to store and manage data. 1.MySQL efficiently processes user information, product catalogs, transaction records and other data. 2. Through SQL query, developers can extract information from the database to generate dynamic content. 3.MySQL works based on the client-server model to ensure acceptable query speed.
Laravel Introduction Example
Apr 18, 2025 pm 12:45 PM
Laravel is a PHP framework for easy building of web applications. It provides a range of powerful features including: Installation: Install the Laravel CLI globally with Composer and create applications in the project directory. Routing: Define the relationship between the URL and the handler in routes/web.php. View: Create a view in resources/views to render the application's interface. Database Integration: Provides out-of-the-box integration with databases such as MySQL and uses migration to create and modify tables. Model and Controller: The model represents the database entity and the controller processes HTTP requests.
How to install mysql in centos7
Apr 14, 2025 pm 08:30 PM
The key to installing MySQL elegantly is to add the official MySQL repository. The specific steps are as follows: Download the MySQL official GPG key to prevent phishing attacks. Add MySQL repository file: rpm -Uvh https://dev.mysql.com/get/mysql80-community-release-el7-3.noarch.rpm Update yum repository cache: yum update installation MySQL: yum install mysql-server startup MySQL service: systemctl start mysqld set up booting
