一次查询多个数据库

Question

我在每个数据库中都有WordPress实例。对于更新我需要查询所有活动的插件，即通过

WHERE option_name='active_plugins' 

存储在表“wp_options”和访问如何访问所有活动插件设置（分布在多个数据库），并在输出一个单一的SQL结果？我知道database.tablename语法，但是我怎么从那里继续使用上面的Where声明？

在一个数据库中的请求是这样的：

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

Answer 1

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Answer 2

通过Pentium10的解决方案是好的，但它的缺点是，你必须扩展查询要包含所有的模式。以下解决方案使用准备好的语句为您的MySQL服务器上的全部模式生成一个结果集，其中有wp_options表。这应该对你更方便。

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

使用过程，游标，联合全部和准备好的语句来查询多个数据库的另一个例子。不需要降和删除权限：

USE `my_db`; 
DROP PROCEDURE IF EXISTS `CountAll`; 
DELIMITER $$ 

CREATE PROCEDURE `CountAll`(IN tableName VARCHAR(255)) 
BEGIN 

    DECLARE db_name   VARCHAR(250); 
    DECLARE exit_loop  BOOLEAN; 
    DECLARE union_query  TEXT DEFAULT ''; 

    DECLARE my_databases CURSOR FOR 
     SELECT DISTINCT `table_schema` 
     FROM `information_schema`.`tables` 
     WHERE 
      `table_schema` LIKE 'myprefix\_%' AND 
      `table_name` = tableName; 

    DECLARE CONTINUE HANDLER 
     FOR NOT FOUND SET exit_loop = TRUE; 

    OPEN my_databases; 

    get_database: LOOP 

     FETCH my_databases INTO db_name; 

     IF exit_loop THEN 
      -- remove trailing UNION ALL statement 
      SET union_query = TRIM(TRAILING ' UNION ALL ' FROM union_query); 
      LEAVE get_database; 
     END IF; 

     SET union_query = concat(union_query, 'SELECT COUNT(*) AS qty FROM ', 
            db_name, '.', tableName, ' UNION ALL '); 

    END LOOP get_database; 

    CLOSE my_databases; 

    SET @final_query = concat('SELECT SUM(qty) FROM (', union_query, 
                ') AS total;'); 
    PREPARE stmt1 FROM @final_query; 
    EXECUTE stmt1; 
    DEALLOCATE PREPARE stmt1; 

END$$ 

DELIMITER ; 

CALL CountAll('wp_options'); 

Answer 4

格鲁伯的答案的伟大工程，但它有一个语法错误---有第10行。这里的最后一个虚假逗号代码，与语法错误修正：

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 
$$