一次查询多个数据库

Question

我在自己的数据库中有每个WordPress实例.对于更新,我需要查询所有活动插件,这些插件存储在表'wp_options'中并可通过

WHERE option_name='active_plugins'

如何访问所有活动的插件设置(分布在多个数据库中)并将它们输出到一个SQL结果中？我知道database.tablename语法,但是如何使用上述Where语句继续？

单个数据库中的请求如下所示:

SELECT option_value
  FROM `database`.`wp_options`
 WHERE option_name="active_plugins"

Answer 1

SELECT option_value
 FROM `database1`.`wp_options`
  WHERE option_name="active_plugins"
UNION
SELECT option_value
 FROM `database2`.`wp_options`
  WHERE option_name="active_plugins"

Answer 2

Pentium10的解决方案很好,但它的缺点是你必须扩展每个要包含的模式的查询.以下解决方案使用预准备语句为MySQL服务器上具有该表的所有模式生成结果集wp_options.这对你来说应该更方便.

DROP PROCEDURE IF EXISTS `MultipleSchemaQuery`;

DELIMITER $$

CREATE PROCEDURE `MultipleSchemaQuery`()
BEGIN
    declare scName varchar(250);
    declare q varchar(2000);

    DROP TABLE IF EXISTS ResultSet;
    create temporary table ResultSet (
     option_value varchar(200)
    );

    DROP TABLE IF EXISTS MySchemaNames;
    create temporary table MySchemaNames (
        schemaName varchar(250)
    );

    insert into MySchemaNames
    SELECT distinct
        TABLE_SCHEMA as SchemaName
    FROM 
        `information_schema`.`TABLES`  
    where 
        TABLE_NAME = 'wp_options';

label1:
    LOOP
        set scName = (select schemaName from MySchemaNames limit 1);
        set @q = concat('select option_value from ', scName, '.wp_options where option_name=\'active_plugins\'');
        PREPARE stmt1 FROM @q;
        EXECUTE stmt1;
        DEALLOCATE PREPARE stmt1;

        delete from MySchemaNames where schemaName = scName;
        IF ((select count(*) from MySchemaNames) > 0) THEN
            ITERATE label1;
        END IF;
        LEAVE label1;

    END LOOP label1;

    SELECT * FROM ResultSet;

    DROP TABLE IF EXISTS MySchemaNames;
    DROP TABLE IF EXISTS ResultSet;
END
$$

DELIMITER ;

CALL MultipleSchemaQuery();

Answer 3

Gruber 的回答很好，但它有一个语法错误 --- 在第 10 行的末尾有一个虚假的逗号。这是代码，修复了语法错误：

DELIMITER $$

CREATE PROCEDURE `MultipleSchemaQuery`()
BEGIN
    declare scName varchar(250);
    declare q varchar(2000);

    DROP TABLE IF EXISTS ResultSet;
    create temporary table ResultSet (
     option_value varchar(200)
    );

    DROP TABLE IF EXISTS MySchemaNames;
    create temporary table MySchemaNames (
        schemaName varchar(250)
    );

    insert into MySchemaNames
    SELECT distinct
        TABLE_SCHEMA as SchemaName
    FROM 
        `information_schema`.`TABLES`  
    where 
        TABLE_NAME = 'wp_options';

label1:
    LOOP
        set scName = (select schemaName from MySchemaNames limit 1);
        set @q = concat('select option_value from ', scName, '.wp_options where option_name=\'active_plugins\'');
        PREPARE stmt1 FROM @q;
        EXECUTE stmt1;
        DEALLOCATE PREPARE stmt1;

        delete from MySchemaNames where schemaName = scName;
        IF ((select count(*) from MySchemaNames) > 0) THEN
            ITERATE label1;
        END IF;
        LEAVE label1;

    END LOOP label1;

    SELECT * FROM ResultSet;

    DROP TABLE IF EXISTS MySchemaNames;
    DROP TABLE IF EXISTS ResultSet;
END
$$