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Efficient SQL test query or validation query that will work across all (or most) databases
...er a little bit of research along with help from some of the answers here:
SELECT 1
H2
MySQL
Microsoft SQL Server (according to NimChimpsky)
PostgreSQL
SQLite
SELECT 1 FROM DUAL
Oracle
SELECT 1 FROM any_existing_table WHERE 1=0
or
SELECT 1 FROM INFORMATION_SCHEMA.SYSTEM_USERS
or
CALL NOW()
HS...
Using DISTINCT and COUNT together in a MySQL Query
...
use
SELECT COUNT(DISTINCT productId) from table_name WHERE keyword='$keyword'
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How do I find which transaction is causing a “Waiting for table metadata lock” state?
...about all the locks transactions are waiting for:
USE INFORMATION_SCHEMA;
SELECT * FROM INNODB_LOCK_WAITS;
A list of blocking transactions:
SELECT *
FROM INNODB_LOCKS
WHERE LOCK_TRX_ID IN (SELECT BLOCKING_TRX_ID FROM INNODB_LOCK_WAITS);
OR
SELECT INNODB_LOCKS.*
FROM INNODB_LOCKS
JOIN INNOD...
Delete all records in a table of MYSQL in phpMyAdmin
...ampserver 2.2. When I want to delete all records of a table in phpMyAdmin (select all) it deletes only one record not all records. Why it does not delete all records?
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What does |= (ior) do in Python?
...ace+ operation between pairs of objects. In particular, between:
sets: a union operation
dicts: an update operation
counters: a union (of multisets) operation
numbers: a bitwise OR, binary operation
In most cases, it is related to the | operator. See examples below.
Sets
For example, the union o...
MySQL get the date n days ago as a timestamp
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DATE_SUB will do part of it depending on what you want
mysql> SELECT DATE_SUB(NOW(), INTERVAL 30 day);
2009-06-07 21:55:09
mysql> SELECT TIMESTAMP(DATE_SUB(NOW(), INTERVAL 30 day));
2009-06-07 21:55:09
mysql> SELECT UNIX_TIMESTAMP(DATE_SUB(NOW(), INTERVAL 30 day));
1244433347
...
How to get database structure in MySQL via query
...CHEMA.TABLES table. It contains metadata about all your tables.
Example:
SELECT * FROM `INFORMATION_SCHEMA`.`TABLES`
WHERE TABLE_NAME LIKE 'table1'
The advantage of this over other methods is that you can easily use queries like the one above as subqueries in your other queries.
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Web API 最佳入门指南 - 更多技术 - 清泛网 - 专注C/C++及内核技术
...他同类型框架的对比，最后通过一些相对复杂的实例展示如何通过WebAPI构建http服务，同时也展示了VisualStudio构建.net项目的各种强大。Web API是一个比较宽泛的概念。这里我们提到Web API特指ASP.NET Web API。
这篇文章中我们主要介绍...
selecting unique values from a column
...
Use the DISTINCT operator in MySQL:
SELECT DISTINCT(Date) AS Date FROM buy ORDER BY Date DESC;
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ERROR: Error 1005: Can't create table (errno: 121)
...y used somewhere else
To check constraints use the following SQL query:
SELECT
constraint_name,
table_name
FROM
information_schema.table_constraints
WHERE
constraint_type = 'FOREIGN KEY'
AND table_schema = DATABASE()
ORDER BY
constraint_name;
Look for more information there,...