"User Defined Variable" 分配为动态字段别名时出错

Question

我在 Workbench 中创建了 MySQL 查询插值。该查询非常适合我的需要，只是我无法将“用户定义变量”@var1/2/3 作为我的字段别名。

我在这一行 AS @var1 上收到错误 (SELECT field4 FROM view_table LIMIT 0, 1) AS @var1 我怀疑字段别名不接受“用户定义的变量”，如我的下面 MySQL 查询：

DROP VIEW IF EXISTS view_table;

CREATE VIEW view_table AS
     SELECT table3.field1, table1.field2
     FROM table1
     JOIN table2 ON table1.table2_id = table2.id
     JOIN table3 ON table1.table3_id = table3.id
     JOIN table4 ON item_var.table4_id = table4.id
     WHERE table2.id = 1
     ORDER BY table1 ASC LIMIT 3;

SET @var1 := (SELECT table3.field1 FROM view_table LIMIT 0, 1);  -- created for the @var1 variable
SET @var2 := (SELECT table3.field1 FROM view_table LIMIT 1, 1);  -- created for the @var2 variable
SET @var3 := (SELECT table3.field1 FROM view_table LIMIT 2, 1);  -- created for the @var3 variable

SELECT table4.field1, table2.field2, table2.field3,
     (SELECT field4 FROM view_table LIMIT 0, 1) AS @var1,  -- @var1 is not recognized as alias
     (SELECT field5 FROM view_table LIMIT 1, 1) AS @var2,  -- @var2 is not recognized as alias
     (SELECT field6 FROM view_table LIMIT 2, 1) AS @var3   -- @var3 is not recognized as alias
FROM table2
JOIN table4 ON table2.id = table4.id
WHERE table2.id = 1;

我要的查询结果如下：

+-------------+------------+------------+------------+------------+-------------+------------+
|name         |Field1      |Field2      |Field3      |@var1       |@var2        |@var3       |
+-------------+------------+------------+------------+------------+-------------+------------+
|XYZ Company  |Field1Data  |Field2Data  |Field3Data  |Field4Data  | Field5Data  |Field6Data  |
+-------------+------------+------------+------------+------------+------------+-------------+

任何人都可以帮助我 figure-out header 变量作为字段别名的正确 MySQL 语法吗？

更新： 我已将解决方案发布在下面以供参考。

Answer 1

终于来了！我得到了解决方案！

我只需要连接上面的最后一个查询就可以插入我创建的字段变量。然后，将其传递到一条语句上，执行该语句并释放它。

SET @statement_var = CONCAT("
SELECT table4.field1, table2.field2, table2.field3, 
    (SELECT field4 FROM view_table LIMIT 0, 1) AS '", @var1, "' ,   
    (SELECT field5 FROM view_table LIMIT 1, 1) AS '", @var1, "' , 
    (SELECT field6 FROM view_table LIMIT 2, 1) AS '", @var1, "' 
FROM table2
JOIN table4 ON item_table2.id = table4.id
WHERE table2.id = 1;");

PREPARE statement FROM @statement_var;

EXECUTE statement;

DEALLOCATE PREPARE statement;

希望这对其他有插值问题的人有所帮助。干杯！

"User Defined Variable" 分配为动态字段别名时出错

Error on "User Defined Variable" assigned as dynamic Field Alias

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