带有单个UNIQUE约束指示符的MySQL列名

Question

我需要一个查询（对于给定的表名）显示带有指示符的列列表，如果此列存在UNIQUE约束，则仅当此列为SINGLE COLUMN约束时，如果此列是多列约束的一部分，则不是。

例如，对于此表：

CREATE TABLE IF NOT EXISTS `prices` (
  `priceId` INT UNSIGNED NOT NULL AUTO_INCREMENT,
  `motorcycleId` INT UNSIGNED NOT NULL,
  `priceDatum` DATE NOT NULL,
  `price` INT NOT NULL DEFAULT 0,
  PRIMARY KEY (`priceId`),
  INDEX `price_motorcycleId_fk_idx` (`motorcycleId` ASC),
  UNIQUE INDEX `priceId_UNIQUE` (`priceId` ASC),
  UNIQUE INDEX `price_UNIQUE` (`motorcycleId` ASC, `priceDatum` ASC),
  CONSTRAINT `price_motorcycleId_fk`
    FOREIGN KEY (`motorcycleId`)
    REFERENCES `motorcycles` (`motorcycleId`)
    ON DELETE CASCADE
    ON UPDATE CASCADE)
ENGINE = InnoDB;

这个查询应该给出：

COLUMN      |UNIQUE
============+======
priceId     |  Y
motorcycleId|  N    <-- should not be shown as UNIQUE since not single constraint
priceDatum  |  N    <-- should not be shown as UNIQUE since not single constraint
price       |  N

Answer 1

您不应该只检查是否存在这样的约束，而且还应检查该约束是否只有一列。因此，KEY_COLUMN_USAGE中该约束的计数应为1。

我现在无法测试它，但它应该看起来像这样得到具有这种约束的列。您可以在子查询中执行类似的操作，或者只是在所有列的列表上连接此查询并检查：如果存在记录，则存在唯一的单列约束，否则不存在。

select
  k.COLUMN_NAME 
from 
  information_schema.KEY_COLUMN_USAGE k
  join information_schema.TABLE_CONSTRAINTS tc
    on k.TABLE_SCHEMA = tc.TABLE_SCHEMA
      and k.TABLE_NAME = tc.TABLE_NAME
      and k.CONSTRAINT_NAME = tc.CONSTRAINT_NAME
where
  k.TABLE_NAME = 'prices'
  and tc.CONSTRAINT_TYPE = 'UNIQUE'
group by
  k.CONSTRAINT_CATALOG,
  k.CONSTRAINT_SCHEMA,
  k.CONSTRAINT_NAME
having
  count(*) = 1

Answer 2

解决方案是：

SELECT c.COLUMN_NAME,
        IF((SELECT COUNT(k2.COLUMN_NAME)
          FROM information_schema.KEY_COLUMN_USAGE k1
          JOIN information_schema.KEY_COLUMN_USAGE k2 
               ON (k1.CONSTRAINT_NAME=k2.CONSTRAINT_NAME
               AND k1.TABLE_NAME=k2.TABLE_NAME
               AND k1.TABLE_SCHEMA=k2.TABLE_SCHEMA)
          JOIN information_schema.TABLE_CONSTRAINTS tc
               ON (k2.CONSTRAINT_NAME=tc.CONSTRAINT_NAME
               AND k2.TABLE_NAME=tc.TABLE_NAME
               AND k2.TABLE_SCHEMA=tc.TABLE_SCHEMA
               AND tc.CONSTRAINT_TYPE='UNIQUE')
         WHERE k1.COLUMN_NAME=c.COLUMN_NAME
           AND k1.TABLE_NAME=c.TABLE_NAME)=1,'Y','N') AS `UNIQUE`
  FROM information_schema.COLUMNS c
  LEFT JOIN information_schema.KEY_COLUMN_USAGE k
   ON (k.TABLE_SCHEMA=c.TABLE_SCHEMA
       AND k.TABLE_NAME=c.TABLE_NAME
       AND k.COLUMN_NAME=c.COLUMN_NAME
       AND k.POSITION_IN_UNIQUE_CONSTRAINT IS NOT NULL)
 WHERE c.TABLE_NAME='prices'
 ORDER BY c.ORDINAL_POSITION