复杂sql语句集锦

本文主要讲一下笔者在工作中遇到的一些逻辑比较复杂的sql语句,下面是具体写法:

SELECT
IF (
    LOCATE('familyKey', link, 1) = 0,
    NULL,
    SUBSTRING(
        link,
        LOCATE('familyKey', link, 1) + LENGTH('familyKey') + 1,

    IF (
        LOCATE(
            '&',
            link,
            LOCATE('familyKey', link, 1)
        ) = 0,
        LENGTH(link),
        LOCATE(
            '&',
            link,
            LOCATE('familyKey', link, 1)
        ) - (
            LOCATE('familyKey', link, 1) + LENGTH('familyKey') + 1
        )
    )
    )
) familyKey
FROM
    illustrations;

　　这条语句是将illustrations表中的link字段，如:

　　...&episType=239&familyKey=90897&illustrationId=6837275...

　　这样的字条串中familyKey=后面的90897这样的编号取出来,说白了就是将字符串按关键字截取,得到的数据可组成新表进行下一步数据分析工作。

我们也可以将其分拆一下，写成下面的语句:

SELECT IF(strbegin=0,NULL,SUBSTRING(link,strbegin+strlen+1,IF(strend=0,LENGTH(link),strend-(strbegin+strlen+1)))) familyKey,mainId
FROM (
SELECT mainId,link,strbegin,LOCATE('&',link,strbegin) strend, LENGTH('familyKey') strlen
FROM (
SELECT mainId,link,LOCATE('familyKey',link,1) strbegin
FROM illustrations
) tmp) tmp;

　　这样看起来就有条理多了，两条语句中都涉及了IF条件判断这些所谓的动态查询的知识点，写完还是小有成就感。

下面介绍一下mysql5.7中的一大亮点改进——对Json数据类型的支持

CREATE TABLE maingroup_id_parentId AS
SELECT n1.id AS parentId,n2.id AS id
FROM nav n1,nav n2
WHERE n1.meta->'$.model' = n2.parent_meta->'$.model'
AND n1.meta->'$.spec' = n2.parent_meta->'$.spec'
AND n1.meta->'$.lang' = n2.parent_meta->'$.lang'
AND n1.meta->'$.startup' = n2.parent_meta->'$.startup'
AND n1.meta->'$.localMarketOnly' = n2.parent_meta->'$.localMarketOnly'
AND n2.nav_table = 'nav-mainGroup-table'
AND n1.nav_table <> 'nav-mainGroup-table';

　　这条语句是将nav表中建立在以model,spec,lang,startup,localMarketOnly这几个关键字为联系的基础上的上下层级关系找出来，建成子表maingroup_id_parentId,然后做进一步数据整理。语句中用到了meta这个Json类型的字段,其使用方式简便、表义清晰，十分适合对类似带数据参数的请求地址的存储。在处理大数据量的表间关系时，上面的用法可能就不实用了,因为效率太差,一条语句可能很久都跑不出来,盲目地等待是没有任何意义的,我是不会做这种事情,所以我们必须找到更高效的关联方案。这里可将这些关键字对应的信息从Json字段中提出来单独作为一个字段，并建立索引，然后将它们进行匹配:

-- pnc字段关键字提取
ALTER TABLE pnc ADD pnc_number VARCHAR(20) generated always AS (json_extract(meta,'$.pnc')) virtual;
ALTER TABLE pnc ADD drawingVar VARCHAR(8) generated always AS (json_extract(meta,'$.drawingVar')) virtual;
ALTER TABLE pnc ADD drawing VARCHAR(8) generated always AS (meta->"$.drawing") virtual;
ALTER TABLE pnc ADD subGroup VARCHAR(8) generated always AS (json_extract(meta,'$.subGroup')) virtual;
ALTER TABLE pnc ADD mainGroup VARCHAR(8) generated always AS (json_extract(meta,'$.mainGroup')) virtual;
ALTER TABLE pnc ADD spec VARCHAR(150) generated always AS (json_extract(meta,'$.spec')) virtual;
ALTER TABLE pnc ADD model VARCHAR(50) generated always AS (json_extract(meta,'$.model')) virtual;
-- pnc建索引
ALTER TABLE pnc ADD INDEX link(pnc_number,drawingVar,drawing,subGroup,mainGroup,spec,model);

-- 修改bom表
ALTER TABLE bom ADD pnc_number VARCHAR(20) generated always AS (json_extract(parent_meta,'$.pnc')) virtual;
ALTER TABLE bom ADD drawingVar VARCHAR(8) generated always AS (json_extract(parent_meta,'$.drawingVar')) virtual;
ALTER TABLE bom ADD drawing VARCHAR(8) generated always AS (parent_meta->"$.drawing") virtual;
ALTER TABLE bom ADD subGroup VARCHAR(8) generated always AS (json_extract(parent_meta,'$.subGroup')) virtual;
ALTER TABLE bom ADD mainGroup VARCHAR(8) generated always AS (json_extract(parent_meta,'$.mainGroup')) virtual;
ALTER TABLE bom ADD spec VARCHAR(150) generated always AS (json_extract(parent_meta,'$.spec')) virtual;
ALTER TABLE bom ADD model VARCHAR(50) generated always AS (json_extract(parent_meta,'$.model')) virtual;
-- bom建索引
ALTER TABLE bom ADD INDEX link(pnc_number,drawingVar,drawing,subGroup,mainGroup,spec,model); 

-- 造表间关系
DROP TABLE IF EXISTS pnc_bom_id;
CREATE TABLE pnc_bom_id
SELECT bom.id AS bomId,pnc.id AS pncId
FROM nissan_bom bom,nissan_pnc pnc
WHERE bom.pnc_number=pnc.pnc_number
AND bom.drawingVar=pnc.drawingVar
AND bom.drawing=pnc.drawing
AND bom.mainGroup=pnc.mainGroup
AND bom.subGroup=pnc.subGroup
AND bom.spec=pnc.spec
AND bom.model=pnc.model;