在 MySQL SELECT "AS" 中使用表名
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Use table name in MySQL SELECT "AS"
提问by preyz
I use the table name to build a nested array when I evaluate my MySQL SELECT JOIN result in PHP. However, when working with AS for calculated columns, I can't seem to set the table name as intended (to simplify, I am trying without a JOIN in this example, but the problem is the same):
当我在 PHP 中评估我的 MySQL SELECT JOIN 结果时，我使用表名来构建嵌套数组。但是，当使用 AS 处理计算列时，我似乎无法按预期设置表名（为简化起见，我在此示例中尝试不使用 JOIN，但问题是相同的）：
SELECT `field1`, `field2`, "Test" AS `Table`.`field3` FROM `Test`;
This throws an error.
这会引发错误。
How can I indicate in the SQL, which table I want to associate field3 with?
如何在 SQL 中指明我想将 field3 与哪个表关联？
(resulting in the table name in $pdoStatement->getColumnMeta()being "Table")
（导致表名$pdoStatement->getColumnMeta()是“表”）
回答by Michael Berkowski
To declare a string literal as an output column, leave the Tableoff and just use Test. It doesn't need to be associated with a table among your joins, since it will be accessed only by its column alias. When using a metadata function like getColumnMeta(), the table name will be an empty string because it isn'tassociated with a table.
要将字符串文字声明为输出列，请Table关闭并使用Test. 它不需要与联接中的表相关联，因为它只能通过其列别名进行访问。当使用元数据函数时getColumnMeta()，表名将是一个空字符串，因为它不与表相关联。
SELECT
`field1`,
`field2`,
'Test' AS `field3`
FROM `Test`;
Note: I'm using single quotes above. MySQL is usually configured to honor double quotes for strings, but single quotes are more widely portable among RDBMS.
注意：我在上面使用单引号。MySQL 通常配置为支持字符串的双引号，但单引号在 RDBMS 中更广泛地可移植。
If you musthave a table alias name with the literal value, you need to wrap it in a subquery with the same name as the table you want to use:
如果你必须有一个带有字面值的表别名，你需要将它包装在一个与你要使用的表同名的子查询中：
SELECT
field1,
field2,
field3
FROM
/* subquery wraps all fields to put the literal inside a table */
(SELECT field1, field2, 'Test' AS field3 FROM Test) AS Test
Now field3will come in the output as Test.field3.
现在field3将作为Test.field3.
回答by Aghilas Yakoub
SELECT field1, field2, 'Test' AS field3FROM Test; // replace with simple quote '
SELECT field1, field2, 'Test' AS field3FROM Test; // 替换为简单的引号 '
