How Can I Use a Variable for a Table Name in a MySQL Stored Procedure?

Using Variables for Table Names in MySQL Stored Procedures

In MySQL, stored procedures enable the execution of pre-defined SQL statements. One common requirement is to pass a table name as a parameter to a stored procedure, allowing it to operate on different tables dynamically.

To utilize a variable for the table name, rather than using the query's literal name, follow these steps:

Step 1: Define the Stored Procedure Parameter

CREATE PROCEDURE `usp_SelectFromTables`(
  IN TableName VARCHAR(100)
)

Here, TableName is the parameter that will hold the table name to be used in the procedure.

Step 2: Convert the Variable Name to a String

During execution, the parameter TableName is a variable. However, SQL statements require strings for table references. To convert the variable to a string, use the CONCAT() function:

Step 3: Concatenate the Variable and Prefix

The table reference in MySQL typically involves a database name, period, and table name. Concatenate this information with the variable using CONCAT() or :

SET @sql_text = CONCAT('SELECT * FROM ', @TableName);

Step 4: Prepare and Execute the Statement

To dynamically execute the prepared SQL statement, use PREPARE and EXECUTE:

PREPARE stmt FROM @sql_text;
EXECUTE stmt;

Example:

Consider the following example, where a dynamic SQL query is constructed based on the value of TableName, cname, and vname:

SET @cname:='jello';
SET @vname:='dwb';
SET @sql_text = CONCAT('select concept_id,concept_name,',@vname,' from enc2.concept a JOIN enc2.ratings b USING(concept_id) where concept_name like (''%',@cname,'%'') and 3 is not null order by 3 asc');

PREPARE stmt FROM @sql_text;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;

By following these steps, you can effectively use a variable to specify the table name in a MySQL stored procedure, enhancing flexibility and reusability.

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