Question

我的TABLE-A具有以下结构：

id      step1error          step2error          step3error
1       null                {json:"string"}     null
2       {json:"error1"}     {json:"error2"}     {json:"error3"}

和具有以下结构的TABLE-B：

id      ref(of TABLE-A)     error
1       1                   null
2       2                   null
3       2                   null
3       2                   null

我尝试了以下查询，但是它始终使用来自TABLE-A的step1error更新TABLE-B。查询：

SET @exist = (select count(TABLE-B.id) from TABLE-B left join TABLE-A on TABLE-B.ref = TABLE-A.id where 
 TABLE-B.error =  TABLE-A.step2error);
UPDATE `TABLE-B` inner join VIEW-AB on TABLE-B.ref=VIEW-AB.ref 
SET TABLE-B.error = 
    CASE 
        WHEN VIEW-AB.step1error != 'null' THEN VIEW-AB.step1error
        WHEN VIEW-AB.step2error != 'null' THEN VIEW-AB.step2error
        ELSE VIEW-AB.step3error END 
WHERE 
TABLE-B.error = 'null' and 
TABLE-B.id = VIEW-AB.B_ref and 
 @exist = 0;

VIEW-AB

create view VIEW-AB as (SELECT  TABLE-B.id "B_ref", TABLE-A.step1error , TABLE-A.step2error, TABLE-A.step3error FROM `TABLE-B` left join TABLE-A on TABLE-B.ref= TABLE-A.id WHERE TABLE-B.error = 'null');

VIEW-AB如下：

B_ref   ref(TABLE-A)    step1error          step2error          step3error
1       1               null              {json:"string"}      null
2       2               {json:"error1"}   {json:"error2"}      {json:"error3"}
3       2               {json:"error1"}   {json:"error2"}      {json:"error3"}
3       2               {json:"error1"}   {json:"error2"}      {json:"error3"}

我的结果：

id      ref(of TABLE-A)     error
1       1                   {json:"string"}
2       2                   {json:"error1"}
3       2                   {json:"error1"}
3       2                   {json:"error1"}

我需要编写一个MySQL查询来更新TABLE-B（错误为null），就像下面这样：

预期结果：

id      ref(of TABLE-A)     error
1       1                   {json:"string"}
2       2                   {json:"error1"}
3       2                   {json:"error2"}
3       2                   {json:"error3"}

Answer 1

更新case语句中的空检查。代替'null'，直接使用null。

因此mysql将'null'视为字符串。

使用以下查询

SET @exist = (select count(TABLE-B.id) from TABLE-B left join TABLE-A on TABLE-B.ref = TABLE-A.id where 
 TABLE-B.error =  TABLE-A.step2error);
UPDATE `TABLE-B` inner join VIEW-AB on TABLE-B.ref=VIEW-AB.ref 
SET TABLE-B.error = 
    CASE 
        WHEN VIEW-AB.step1error is not null THEN VIEW-AB.step1error
        WHEN VIEW-AB.step2error is not null THEN VIEW-AB.step2error
        ELSE VIEW-AB.step3error END 
WHERE 
TABLE-B.error = 'null' and 
TABLE-B.id = VIEW-AB.B_ref and 
 @exist = 0;

如何在某些条件下从另一个表更新MySQL表

1 个答案: