如何检查MySQL中的表字段上是否存在索引?

使用 SHOW INDEX 像这样:

SHOW INDEX FROM [tablename]

https://dev.mysql.com/doc/refman/5.0/en/show-index.html

尝试:

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

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

您可以找到表中是否存在唯一的键

show index from table_name where Column_name='column_name';

使用以下语句:SHOW INDEX FROM 你的桌子

确保您正确填写了“密钥名称”

仅从cli查看表布局。你会的

描述我的表格

或

使用以下语句:从您的_表中显示索引

然后检查字段的结果:行[“表”],

确保您正确填写了“密钥名称”

您可以将其转换为PHP(或其他语言),并围绕sql语句查找索引列。基本上,您可以将SHOW INDEX的结果从“mytable”拉入PHP,然后使用列“column\u name”获取索引列。

创建数据库连接字符串并执行以下操作:

$mysqli = mysqli_connect("localhost", "my_user", "my_password", "world");

$sql =  "SHOW INDEX FROM 'mydatabase.mytable' WHERE Key_name = 'PRIMARY';" ;
$result = mysqli_query($mysqli, $sql);

while ($row = $result->fetch_assoc()) {
    echo $rowVerbatimsSet["Column_name"];
}

您可以使用下面的SQL语句检查表上的给定列是否已编制索引

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;

因为连接是针对INNODB_SYS_*的,所以匹配索引只来自INNODB表

如果您需要一个列的索引作为数据库函数存在的功能(这里是按顺序排列的第一位),您可以使用/采用此代码。 如果您想检查索引是否存在,而不管它在多列索引中的位置如何,那么只需删除部分“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 ;

尝试使用以下方法:

SELECT TRUE
FROM INFORMATION_SCHEMA.KEY_COLUMN_USAGE 
WHERE TABLE_SCHEMA = "{DB_NAME}" 
AND TABLE_NAME = "{DB_TABLE}"
AND COLUMN_NAME = "{DB_INDEXED_FIELD}";

无法运行特定的显示索引查询,因为如果索引不存在,它将抛出错误。因此,如果要避免任何SQL错误,必须将所有索引抓取到一个数组中并循环遍历它们。

我是这样做的。我从表中获取所有索引(在本例中, leads 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;
    }
}

通过这种方式,您可以真正缩小索引属性的范围。做一个 print_r 属于 $res 看看你能用什么。