大约有 46,000 项符合查询结果（耗时：0.0321秒） [XML]
How to declare a variable in a PostgreSQL query
...ows you to return a table of temporary values.
WITH master_user AS (
SELECT
login,
registration_date
FROM users
WHERE ...
)
SELECT *
FROM users
WHERE master_login = (SELECT login
FROM master_user)
AND (SELECT registration_date
FROM ma...
How to select bottom most rows?
I can do SELECT TOP (200) ... but why not BOTTOM (200)?
14 Answers
14
...
How to take MySQL database backup using MySQL Workbench?
...ble) within Server Administration.
Steps to Create New Server Instance:
Select New Server Instance option within Server Administrator.
Provide connection details.
After creating new server instance , it will be available in Server Administration list. Double click on Server instance you have cr...
Get table names using SELECT statement in MySQL
...
To get the name of all tables use:
SELECT table_name FROM information_schema.tables;
To get the name of the tables from a specific database use:
SELECT table_name FROM information_schema.tables
WHERE table_schema = 'your_database_name';
Now, to answer the...
Join vs. sub-query
...
@JinghuiNiu Customers who bought expensive items: select custid from cust join bought using (custid) where price > 500. If a customer bought multiple expensive items, you'll get double-ups. To fix this, select custid from cust where exists (select * from bought where cust...
Create table (structure) from existing table
...
Try:
Select * Into <DestinationTableName> From <SourceTableName> Where 1 = 2
Note that this will not copy indexes, keys, etc.
If you want to copy the entire structure, you need to generate a Create Script of the tab...
How to concatenate columns in a Postgres SELECT?
... an explicit coercion to text [...]
Bold emphasis mine. The 2nd example (select a||', '||b from foo) works for any data types since the untyped string literal ', ' defaults to type text making the whole expression valid in any case.
For non-string data types, you can "fix" the 1st statement by c...
'IF' in 'SELECT' statement - choose output value based on column values
...
SELECT id,
IF(type = 'P', amount, amount * -1) as amount
FROM report
See http://dev.mysql.com/doc/refman/5.0/en/control-flow-functions.html.
Additionally, you could handle when the condition is null. In the case of...
MySQL: Set user variable from result of query
...need to move the variable assignment into the query:
SET @user := 123456;
SELECT @group := `group` FROM user WHERE user = @user;
SELECT * FROM user WHERE `group` = @group;
Test case:
CREATE TABLE user (`user` int, `group` int);
INSERT INTO user VALUES (123456, 5);
INSERT INTO user VALUES (111111...
How do you use script variables in psql?
...t myvariable value
... and can then be substituted, for example, as ...
SELECT * FROM :myvariable.table1;
... or ...
SELECT * FROM table1 WHERE :myvariable IS NULL;
edit: As of psql 9.1, variables can be expanded in quotes as in:
\set myvariable value
SELECT * FROM table1 WHERE column1 ...