mysql如何使DROP INDEX IF EXISTS存在？

Question

我想用IF EXISTS选项在mysql中删除索引，但没有发现任何使它起作用的东西。

DROP INDEX IF EXISTS index_name ON table_name;

有人有提示吗？

Answer 1

我没有看到任何直接的DROP INDEX使用方法IF EXISTS。作为解决方法，我编写了以下程序，该程序对我有用。

CREATE PROCEDURE `DropIndexIfExists`(
    IN i_table_name VARCHAR(128),
    IN i_index_name VARCHAR(128)
    )
    BEGIN

    SET @tableName = i_table_name;
    SET @indexName = i_index_name;
    SET @indexExists = 0;

    SELECT 
        1
    INTO @indexExists FROM
        INFORMATION_SCHEMA.STATISTICS
    WHERE
        TABLE_NAME = @tableName
            AND INDEX_NAME = @indexName;

    SET @query = CONCAT(
        'DROP INDEX ', @indexName, ' ON ', @tableName
    );
    IF @indexExists THEN
        PREPARE stmt FROM @query;
        EXECUTE stmt;
        DEALLOCATE PREPARE stmt;
    END IF;
    END

Answer 2

尝试这个，

create procedure DeleteIndex()
begin

IF EXISTS ( SELECT * FROM INFORMATION_SCHEMA.STATISTICS  WHERE TABLE_NAME = 'TableName'
            AND INDEX_NAME = 'IndexName' AND INDEX_SCHEMA='DbName') THEN
   ALTER TABLE  TableName DROP index THead2;
END IF;
END