Today reading about MySQL Table Locking Issues. Of particular interest were the HIGH_PRIORITY and SQL_BUFFER_RESULT SELECT Statement options.
Tag Archives: mysql
Omitting date completed from MySQL dump file
By default when you run a dump with ‘mysqldump’ the date of the dump is appended to the file, e.g.:
jj5@love:~/desktop/experiment$ udiff * --- dbt__jj_dev_1__svn_jdrepo.1.sql 2019-06-11 18:11:13.267758230 +1000 +++ dbt__jj_dev_1__svn_jdrepo.2.sql 2019-06-11 18:12:03.856075974 +1000 @@ -32,4 +32,4 @@ /*!40101 SET COLLATION_CONNECTION=@OLD_COLLATION_CONNECTION */; /*!40111 SET SQL_NOTES=@OLD_SQL_NOTES */; --- Dump completed on 2019-06-10 21:59:44 +-- Dump completed on 2019-06-10 12:06:49
This causes dumps for a single database that has not changed to have two dumps which differ. It’s better to have dumps from the same unchanged database to be the same. To facilitate that add the –skip-dump-date option when running ‘mysqldump’.
See here for the back-story.
PDO: Execute a prepared statement using array for IN clause
See Example #5 here.
/* Execute a prepared statement using an array of values for an IN clause */
$params = array(1, 21, 63, 171);
/* Create a string for the parameter placeholders filled to the number of params */
$place_holders = implode(',', array_fill(0, count($params), '?'));
/*
This prepares the statement with enough unnamed placeholders for every value
in our $params array. The values of the $params array are then bound to the
placeholders in the prepared statement when the statement is executed.
This is not the same thing as using PDOStatement::bindParam() since this
requires a reference to the variable. PDOStatement::execute() only binds
by value instead.
*/
$sth = $dbh->prepare("SELECT id, name FROM contacts WHERE id IN ($place_holders)");
$sth->execute($params);
Running a SQL text file in mysql CLI
Reply
Use the ‘source’ command:
mysql> source path/to/file.sql
Calculate a median with MySQL
Today I read this article and found this technique for calculating a median value:
SELECT x.val from data x, data y GROUP BY x.val HAVING SUM(SIGN(1-SIGN(y.val-x.val)))/COUNT(*) > .5 LIMIT 1
MySQL convert_tz
Today I used the MySQL convert_tz function.
Before I could use named timezones with convert_tz I had to load the timezones.
Loading MySQL timezone data
Turns out MySQL doesn’t load timezone info by default! As you can read about here.
To load MySQL timezone info:
mysql_tzinfo_to_sql /usr/share/zoneinfo | mysql -u root -p mysql
PostgreSQL LIMIT and OFFSET
Today I learned about LIMIT and OFFSET in PostgreSQL, which differs slightly from its MySQL cousin.
psql show tables
I wanted to know what the analogue for MySQL ‘show tables’ was in PostgreSQL, and I found the answer, use the information_schema, here:
mysql: SHOW TABLES postgresql: \d postgresql: SELECT table_name FROM information_schema.tables WHERE table_schema = 'public'; mysql: SHOW DATABASES postgresql: \l postgresql: SELECT datname FROM pg_database; mysql: SHOW COLUMNS postgresql: \d table postgresql: SELECT column_name FROM information_schema.columns WHERE table_name ='table'; mysql: DESCRIBE TABLE postgresql: \d+ table postgresql: SELECT column_name FROM information_schema.columns WHERE table_name ='table';
MySQL Integer Types
Reading about MySQL Integer Types.