What is used to express conditions in sql

The WHERE keyword expressing conditions in SQL allows you to filter records by specifying conditions, limiting the data to be retrieved based on specific columns or expression values. WHERE condition types include equality conditions, inequality conditions, comparison conditions, Boolean conditions, null conditions, LIKE conditions, IN conditions, and BETWEEN conditions.

Keywords expressing conditions in SQL

The WHERE keyword is used to specify conditions in SQL statements to Filter out records that meet specific criteria. It allows you to limit the data to be retrieved based on the value of a specific column or expression.

WHERE statement syntax:

<code class="sql">SELECT column_list
FROM table_name
WHERE condition;</code>

WHERE condition type:

• Equal value condition : Check whether the column value is equal to the specified value. For example: WHERE age = 25
• Unequal value condition: Check whether the column value is not equal to the specified value. For example: WHERE age <> 30
• Comparison conditions: Compare column values ​​with other values ​​or column values. For example: WHERE salary > 50000
• Boolean condition: Use Boolean operators (AND, OR, NOT) Combine multiple conditions. For example: WHERE (age > 25) AND (salary > 50000)
• Null value condition: Check whether the column value is NULL or NOT NULL. For example: WHERE name IS NULL
• LIKE condition: Use wildcard characters (% and _) to match string values a part of. For example: WHERE name LIKE '%John%'
• IN Condition: Checks whether the column value is included in the specified value list. For example: WHERE id IN (1, 2, 3)
• BETWEEN Condition: Check whether the column value is within the specified range. For example: WHERE age BETWEEN 20 AND 30

Example:

The following SQL statement is based on the age column Value Retrieve all records older than 25 years old:

<code class="sql">SELECT *
FROM employees
WHERE age > 25;</code>

Using WHERE conditions allows you to efficiently retrieve data that meets specific criteria from a database table, which is critical for filtering and querying data.

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