What does from dual mean in mysql

FROM DUAL is used in MySQL to retrieve data from a single-row virtual table DUAL, often used to get the current date and time, database version, or as a placeholder in a query or to execute a DDL statement.

FROM DUAL in MySQL

Question: What is FROM DUAL in MySQL mean?

Answer:

FROM DUAL is used in MySQL to retrieve data from a virtual table DUAL that contains a single row. It is often used to perform queries or obtain metadata information without the actual data table.

Detailed explanation:

The DUAL table is a special virtual table that does not contain any data but always exists in the database. It contains one row with the column name DUMMY.

When you use the FROM DUAL statement to retrieve data from the DUAL table, it returns the value of that single row, which is DUMMY. This value is typically used as a placeholder or constant to help construct queries.

The FROM DUAL statement has the following uses:

• Get the current date and time: Use the NOW() function, such as SELECT NOW() FROM DUAL .
• Get the database version: Use the VERSION() function, such as SELECT VERSION() FROM DUAL.
• As a placeholder in a subquery: For example, it can be used to get an empty result set to join to another table, such as SELECT * FROM table1 WHERE id IN ( SELECT DUMMY FROM DUAL).
• Execute DDL statements: For example, it can be used to create or delete tables, such as CREATE TABLE table1 (id INT) FROM DUAL.

Syntax:

<code class="sql">SELECT <expression>
FROM DUAL;</code>

Where is the value or function to be returned.

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