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SQL

The role of round in sql

The ROUND function is used to round a number to a specified number of decimal places, with the syntax ROUND(number, decimals). Its functions include formatting numbers, calculating based on precision, and creating derived columns with a specified number of decimal places.

May 01, 2024 pm 11:09 PM

How to express not equal to empty in sql

There are two ways to write not equal to null in SQL: 1. IS NOT NULL; 2. <> ''. Using the IS NOT NULL query will return records where the column is not NULL, while using the <> '' query will return records where the column is not equal to the empty string.

May 01, 2024 pm 11:09 PM

Function that converts multi-row values into one row in sql

The function in SQL that converts multiple rows of values into one row is ARRAY_TO_STRING(), which converts an array into a comma-separated string. Used in conjunction with aggregate functions such as GROUP_CONCAT(), data from multiple rows can be grouped and converted into a single row.

May 01, 2024 pm 11:06 PM

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How to write multiple likes in sql

In SQL, you can use multiple LIKE conditions to match partially matched string values. You can use the following method: Use the OR operator to connect multiple LIKE conditions to match rows that meet any condition. Use the IN operator to specify a list of values, matching a condition where the column value matches an exact value in the list. Use subqueries to create subsets, and then match multiple strings through the main query.

May 01, 2024 pm 11:06 PM

How to use escape in mysql

The ESCAPE keyword is used to specify escape characters to escape special characters in a string before they are recognized as metacharacters or delimiters. It immediately precedes the escaped string, using the format: ESCAPE 'escape character'. By default, ESCAPE escapes backslashes, percent signs, underscores, single quotes, double quotes, backtick marks, spaces, tabs, newlines, and carriage returns.

May 01, 2024 pm 11:06 PM

mysql

What does ll mean in sql

LL in SQL stands for list of lists, which is used to combine the results of multiple subqueries or derived tables into a single result set in a SELECT statement to improve code readability, performance, and modularity.

May 01, 2024 pm 11:03 PM

The difference between all and any in sql

ALL and ANY in SQL compare the results of a subquery to the results of the main query. ALL requires the subquery to return true for every row, while ANY requires only that it return true for at least one row. Therefore, the ALL comparison is more strict and is typically used to determine if all conditions are met, while the ANY comparison is more relaxed and is used to determine if at least one condition is met.

May 01, 2024 pm 11:03 PM

What does any mean in sql

The ANY keyword in SQL is used to check whether a subquery returns any rows that satisfy a given condition: Syntax: ANY (subquery) Usage: Used with comparison operators, if the subquery returns any rows that satisfy the condition, the ANY expression Evaluates to true Advantages: simplifies queries, improves efficiency, and is suitable for processing large amounts of data Limitations: does not provide specific rows that meet the condition, if the subquery returns multiple rows that meet the condition, only true is returned

May 01, 2024 pm 11:03 PM

sql优化

What does FILENAME mean in sql

The FILENAME function returns a file path and file name string in SQL and can be used to obtain the file path, determine whether the file exists, and load the file contents into a table.

May 01, 2024 pm 11:00 PM

What to use instead of in in sql

Alternatives to the IN operator in SQL include the EXISTS subquery, CASE expressions, and the OR operator. The choice of an alternative depends on factors such as performance, flexibility, maintainability, etc. Usually the IN operator is preferred, but the alternatives provide a better solution in some cases.

May 01, 2024 pm 10:57 PM

The difference between in and = in sql

IN and = are different operators used to compare values in SQL. IN is used to check if a value belongs to a specific set of values, while = is used to compare two separate values.

May 01, 2024 pm 10:57 PM

The meaning of in in sql

The IN operator checks whether a value is included in the specified value list. The syntax is: SELECT * FROM table_name WHERE column_name IN (value1, value2, ..., valueN). It has the advantage of improving query performance, especially when you need to check whether a value is contained in a large number of values. Additionally, the IN operator can be used with a subquery or NOT operator.

May 01, 2024 pm 10:54 PM

Statements to view tables in mysql

MySQL provides a variety of statements for viewing table information: View table structure: DESCRIBE table name View table data: SELECT * FROM table name View table information: SHOW TABLE STATUS LIKE "table name" View table index: SHOW INDEX FROM table name View table constraints : SHOW CREATE TABLE table name

May 01, 2024 pm 10:54 PM

mysql

What is a non-aggregated column in sql

Non-aggregated columns in SQL are columns that store single record values and are not processed by aggregate functions. These columns contain unique values for each record and are used to identify, categorize, or filter the data.

May 01, 2024 pm 10:51 PM

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