我想通过使用ALTER
语法向表中添加索引,但首先检查它是否已存在于表中,并且仅在索引不存在时添加索引。
ALTER TABLE tableName ADD INDEX IX_Table_XYZ (column1);
有没有办法做到这一点?
试试这样:
set @x := (select count(*) from information_schema.statistics where table_name = 'table' and index_name = 'IX_Table_XYZ' and table_schema = database());
set @sql := if( @x > 0, 'select ''Index exists.''', 'Alter Table TableName ADD Index IX_Table_XYZ (column1);');
PREPARE stmt FROM @sql;
EXECUTE stmt;
您可以使用此语法检查索引(按索引名称)是否存在
SELECT 1
FROM INFORMATION_SCHEMA.STATISTICS
WHERE TABLE_SCHEMA = 'yourschema' AND TABLE_NAME='yourtable' AND
INDEX_NAME='yourindex';
然后你可以在存储过程中运行它
IF (SELECT 1
FROM INFORMATION_SCHEMA.STATISTICS
WHERE TABLE_SCHEMA = 'yourschema' AND TABLE_NAME='yourtable' AND
INDEX_NAME='yourindex') != 1 THEN
Alter Table TableName ADD Index IX_Table_XYZ (column1);
END IF;
基于@KayNelson的回答,对我来说,在MySQL 5.7.16中,正确的方法是在IS NULL
条件下使用!=1
而不是IF
。
所以有条件地将INDEX
添加到表中的片段是:
IF (SELECT 1
FROM `INFORMATION_SCHEMA`.`STATISTICS`
WHERE `TABLE_SCHEMA` = 'yourschema'
AND `TABLE_NAME` = 'yourtable'
AND `INDEX_NAME` = 'yourindex') IS NULL THEN
ALTER TABLE `yourtable` ADD INDEX `yourindex` (`column1` ASC);
END IF;