大约有 40,000 项符合查询结果（耗时：0.0253秒） [XML]
How can I select random files from a directory in bash?
I have a directory with about 2000 files. How can I select a random sample of N files through using either a bash script or a list of piped commands?
...
PostgreSQL function for last inserted ID
...e:
INSERT INTO persons (lastname,firstname) VALUES ('Smith', 'John');
SELECT currval('persons_id_seq');
The name of the sequence must be known, it's really arbitrary; in this example we assume that the table persons has an id column created with the SERIAL pseudo-type. To avoid relying on thi...
Postgresql GROUP_CONCAT equivalent?
...
This is probably a good starting point (version 8.4+ only):
SELECT id_field, array_agg(value_field1), array_agg(value_field2)
FROM data_table
GROUP BY id_field
array_agg returns an array, but you can CAST that to text and edit as needed (see clarifications, below).
Prior to version...
MySQL: Quick breakdown of the types of joins [duplicate]
...es
END EDIT
In a nutshell, the comma separated example you gave of
SELECT * FROM a, b WHERE b.id = a.beeId AND ...
is selecting every record from tables a and b with the commas separating the tables, this can be used also in columns like
SELECT a.beeName,b.* FROM a, b WHERE b.id = a.beeId...
Pipe to/from the clipboard in Bash script
...lets you talk to it.
In the case of X, there's xclip (and others). xclip -selection c will send data to the clipboard that works with Ctrl + C, Ctrl + V in most applications.
If you're on Mac OS X, there's pbcopy. e.g cat example.txt | pbcopy
If you're in Linux terminal mode (no X) then look into...
Simulate CREATE DATABASE IF NOT EXISTS for PostgreSQL?
...k around it from within psql by executing the DDL statement conditionally:
SELECT 'CREATE DATABASE mydb'
WHERE NOT EXISTS (SELECT FROM pg_database WHERE datname = 'mydb')\gexec
The manual:
\gexec
Sends the current query buffer to the server, then treats each column of each row of the query's outpu...
Query grants for a table in postgres
...
I already found it:
SELECT grantee, privilege_type
FROM information_schema.role_table_grants
WHERE table_name='mytable'
share
|
improve this...
Keeping it simple and how to do multiple CTE in a query
...s in one query, as well as reuse a CTE:
WITH cte1 AS
(
SELECT 1 AS id
),
cte2 AS
(
SELECT 2 AS id
)
SELECT *
FROM cte1
UNION ALL
SELECT *
FROM cte2
UNION ALL
SELECT *
FROM cte1
Note, however, that SQL Server may reevaluate t...
SQL - HAVING vs. WHERE
...ows; HAVING clause introduces a condition on aggregations, i.e. results of selection where a single result, such as count, average, min, max, or sum, has been produced from multiple rows. Your query calls for a second kind of condition (i.e. a condition on an aggregation) hence HAVING works correctl...
How do I cast a string to integer and have 0 in case of error in the cast with PostgreSQL?
...dn't want the overhead of a function. I came up with the following query:
SELECT myfield::integer FROM mytable WHERE myfield ~ E'^\\d+$';
Postgres shortcuts its conditionals, so you shouldn't get any non-integers hitting your ::integer cast. It also handles NULL values (they won't match the regex...