如何检查MySQL中的表字段是否存在索引？

Question

我需要Google几次，所以我正在分享我的问答。

Answer 1

使用 SHOW INDEX ，如下所示：

SHOW INDEX FROM [tablename]

文档： https://dev.mysql.com/ DOC / refman / 5.0 / EN /显示-的index.html

Answer 2

尝试：

SELECT * FROM information_schema.statistics 
  WHERE table_schema = [DATABASE NAME] 
    AND table_name = [TABLE NAME] AND column_name = [COLUMN NAME]

它会告诉您某个列上是否存在任何类型的索引，而无需知道为索引指定的名称。它也可以在存储过程中工作（而不是显示索引）

Answer 3

SHOW KEYS FROM  tablename WHERE Key_name='unique key name'

您可以找到表格中是否存在唯一键

Answer 4

show index from table_name where Column_name='column_name';

Answer 5

使用以下语句：SHOW INDEX FROM your_table

然后检查字段的结果：row [＆quot; Table＆quot;]，row [＆quot; Key_name＆quot;]

请务必写下“Key_name”正确

Answer 6

只是从cli看一下表格布局。你会做的

  

desc mytable

或

  

show table mytable

Answer 7

如果您需要该功能，如果列的索引存在（此处在序列的第一位）作为数据库函数，您可以使用/采用此代码。 如果要检查索引是否存在，而不管多列索引中的位置如何，则只需删除部分“AND SEQ_IN_INDEX = 1”。

DELIMITER $
CREATE FUNCTION `fct_check_if_index_for_column_exists_at_first_place`(
    `IN_SCHEMA` VARCHAR(255),
    `IN_TABLE` VARCHAR(255),
    `IN_COLUMN` VARCHAR(255)
)
RETURNS tinyint(4)
LANGUAGE SQL
DETERMINISTIC
CONTAINS SQL
SQL SECURITY DEFINER
COMMENT 'Check if index exists at first place in sequence for a given column in a given table in a given schema. Returns -1 if schema does not exist. Returns -2 if table does not exist. Returns -3 if column does not exist. If index exists in first place it returns 1, otherwise 0.'
BEGIN

-- Check if index exists at first place in sequence for a given column in a given table in a given schema. 
-- Returns -1 if schema does not exist. 
-- Returns -2 if table does not exist. 
-- Returns -3 if column does not exist. 
-- If the index exists in first place it returns 1, otherwise 0.
-- Example call: SELECT fct_check_if_index_for_column_exists_at_first_place('schema_name', 'table_name', 'index_name');

-- check if schema exists
SELECT 
    COUNT(*) INTO @COUNT_EXISTS
FROM 
    INFORMATION_SCHEMA.SCHEMATA
WHERE 
    SCHEMA_NAME = IN_SCHEMA
;

IF @COUNT_EXISTS = 0 THEN
    RETURN -1;
END IF;


-- check if table exists
SELECT 
    COUNT(*) INTO @COUNT_EXISTS
FROM 
    INFORMATION_SCHEMA.TABLES
WHERE 
    TABLE_SCHEMA = IN_SCHEMA
AND TABLE_NAME = IN_TABLE
;

IF @COUNT_EXISTS = 0 THEN
    RETURN -2;
END IF;


-- check if column exists
SELECT 
    COUNT(*) INTO @COUNT_EXISTS
FROM 
    INFORMATION_SCHEMA.COLUMNS
WHERE 
    TABLE_SCHEMA = IN_SCHEMA
AND TABLE_NAME = IN_TABLE
AND COLUMN_NAME = IN_COLUMN
;

IF @COUNT_EXISTS = 0 THEN
    RETURN -3;
END IF;

-- check if index exists at first place in sequence
SELECT 
    COUNT(*) INTO @COUNT_EXISTS
FROM 
    information_schema.statistics 
WHERE 
    TABLE_SCHEMA = IN_SCHEMA
AND TABLE_NAME = IN_TABLE AND COLUMN_NAME = IN_COLUMN
AND SEQ_IN_INDEX = 1;


IF @COUNT_EXISTS > 0 THEN
    RETURN 1;
ELSE
    RETURN 0;
END IF;


END$
DELIMITER ;

Answer 8

您可以使用以下SQL语句来检查表上的给定列是否已编入索引

select  a.table_schema, a.table_name, a.column_name, index_name
from    information_schema.columns a
join    information_schema.tables  b on a.table_schema  = b.table_schema and
                                    a.table_name = b.table_name and 
                                    b.table_type = 'BASE TABLE'
left join (
 select     concat(x.name, '/', y.name) full_path_schema, y.name index_name
 FROM   information_schema.INNODB_SYS_TABLES  as x
 JOIN   information_schema.INNODB_SYS_INDEXES as y on x.TABLE_ID = y.TABLE_ID
 WHERE  x.name = 'your_schema'
 and    y.name = 'your_column') d on concat(a.table_schema, '/', a.table_name, '/', a.column_name) = d.full_path_schema
where   a.table_schema = 'your_schema'
and     a.column_name  = 'your_column'
order by a.table_schema, a.table_name;

由于连接是针对INNODB_SYS_ *的，因此匹配索引仅来自INNODB表

Answer 9

您无法运行特定的show index查询，因为如果索引不存在，它将引发错误。因此，如果要避免任何SQL错误，必须将所有索引都捕获到数组中并循环遍历它们。

继承人我是怎么做到的。我从表中获取所有索引（在本例中为 leads ），然后在foreach循环中检查列名称（在本例中为 province ）存在与否。

$this->name = 'province';

$stm = $this->db->prepare('show index from `leads`');
$stm->execute();
$res = $stm->fetchAll();
$index_exists = false;

foreach ($res as $r) {
    if ($r['Column_name'] == $this->name) {
        $index_exists = true;
    }
}

这样你就可以真正缩小索引属性。执行 $ res 的 print_r ，以查看可以使用的内容。