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SQL

How to use if in sql

The IF statement is used for conditional execution in SQL. Its syntax is: IF condition THEN true_statement [ELSE false_statement] END IF; usage includes: selecting and executing different SQL statement blocks based on conditions, such as dynamically displaying messages based on age, updating records, and deleting records. Or set variables.

May 01, 2024 pm 10:45 PM

Usage of is null in sql

IS NULL is an operator in SQL that checks whether a field or expression is a NULL value. The syntax is "Field IS NULL" or "Expression IS NULL". It is often used to check whether a field is NULL, compare NULL values to other values, or exclude rows with NULL values from the result set.

May 01, 2024 pm 10:42 PM

What does isnull mean in sql

The ISNULL function checks whether an expression is NULL and returns the specified replacement value if it is, otherwise it returns the expression itself. The main uses include: 1. Replace NULL values with non-NULL values; 2. Avoid data conversion errors; 3. Display meaningful values.

May 01, 2024 pm 10:42 PM

The difference between null value and null in sql

In SQL, NULL represents unknown data, while a null value represents an unassigned value. The difference between NULL and null values lies in semantic meaning (NULL is unambiguously missing, and null values do not require semantics), performance efficiency (NULL processing is more efficient), and query results (NULL comparison results are unpredictable). Determine NULL and null values via IS NULL, IS NOT NULL, or COALESCE. Best practices are to explicitly use NULL to indicate missing data, avoid using null values, and handle NULL values wisely.

May 01, 2024 pm 10:42 PM

mysql

When usage in sql

The WHEN clause in SQL is used to specify conditions in a CASE expression and return the corresponding output. The syntax is as follows: CASE WHEN condition THEN result END. When the condition is TRUE, the corresponding result is returned.

May 01, 2024 pm 10:39 PM

What can be used instead of case when in sql

CASE WHEN in SQL can be replaced by the IF() function. IF() function syntax: IF(condition, value_if_true, value_if_false). Advantages: concise syntax, high readability, and good scalability. Note, however, that some DBMSs may not support the IF() function.

May 01, 2024 pm 10:39 PM

case when usage in plsql

CASE WHEN in PL/SQL is a conditional statement that performs different actions based on conditions. Syntax: CASE WHEN condition THEN result ELSE default result END; Advantages: more concise, easy to read, and can be nested. Limitation: Only single value conditions can be processed, the result must be a single value.

May 01, 2024 pm 10:36 PM

How to write division in sql

SQL division uses the / operator. When the divisor is an integer, the integer is returned and the decimal is discarded. When the divisor is a decimal, the floating point is returned and the decimal place is retained. Dividing by 0 will report an error, and the result will be negative if the sign is different. You can use the ROUND() function to preserve a specified number of decimal places, and convert the number to floating point to avoid loss of precision.

May 01, 2024 pm 10:33 PM

How to calculate division with decimals in SQL

SQL division method to preserve decimals: use CAST, ROUND or TRUNCATE function. The CAST function coerces a numeric type to preserve specific precision and scale. The ROUND function rounds floating point results. The TRUNCATE function truncates floating point results.

May 01, 2024 pm 10:33 PM

Usage of if statement after where in sql

The IF statement is used in the SQL WHERE clause to create a conditional expression that performs different actions based on a certain condition. It can replace null values with another value, return different values based on conditions, and perform nested queries based on different conditions.

May 01, 2024 pm 10:31 PM

What are the conditional judgment statements in sql

Conditional judgment statements in SQL are used to determine whether conditions are true or false and perform corresponding operations. There are two main types: IF-ELSE statement: different statements are executed depending on whether the condition is true or false. CASE statement: Returns different results based on conditional matching.

May 01, 2024 pm 10:30 PM

What can be used to replace in in sql

The alternatives to IN in SQL are: 1. EXISTS subquery checks the existence of values in other tables; 2. Subqueries use comparison operators to compare subquery values; 3. JOIN uses JOIN conditions to compare values; 4. UNION uses The combined results of UNION and DISTINCT are similar to IN after deduplication. Consider data volume, complexity, and readability when choosing a solution.

May 01, 2024 pm 10:30 PM

What data type does id in sql belong to?

IDs in SQL are typically integer types, including INT, UNSIGNED INT, and BIGINT, or char(36) character fields. Consider expected value range, storage space, processing speed, and uniqueness requirements when selecting. INT or UNSIGNED INT are common choices, BIGINT for handling very large or small values, and CHAR(36) for storing unique identifiers such as UUIDs.

May 01, 2024 pm 10:27 PM

The role of $ in sql

The $ symbol in SQL has three functions: to represent parameter placeholders, such as SELECT * FROM users WHERE id = $1; to escape special characters, such as SELECT * FROM users WHERE name = '$name'; to represent variables, such as in PostgreSQL , $$name$$ represents session variables.

May 01, 2024 pm 10:24 PM