Rails 4 makes this too easy 🙂 Foo.where.not(id: Bar.select(:foo_id).uniq) this outputs the same query as jdoe’s answer SELECT “foos”.* FROM “foos” WHERE “foos”.”id” NOT IN ( SELECT DISTINCT “bars”.”foo_id” FROM “bars” ) And as a scope: scope :lonely, -> { where.not(id: Bar.select(:item_id).uniq) }
You should use psql command line tool: psql -h hostname -p port_number -U username -f your_file.sql databasename
Duplicate your table into a table to be archived: SELECT * INTO ArchiveTable FROM MyTable Delete all entries in your table: DELETE * FROM MyTable
To insert into only one column, use only one piece of data: INSERT INTO Data ( Col1 ) VALUES (‘Hello World’); Alternatively, to insert multiple records, separate the inserts: INSERT INTO Data ( Col1 ) VALUES (‘Hello’), (‘World’);
A table can have just one primary key constraint, but that may be comprised of several columns e.g. create table my_table (col1 integer, col2 integer, col3 integer, primary key (col1, col2, col3) ); In addition to the primary key, a table may also have one or more UNIQUE constraints, e.g. create table my_table2 (col1 integer, … Read more
SELECT * FROM mixedvalues WHERE value REGEXP ‘^[0-9]+$’;
use select to_char(date_column,’YYYY-MM-DD’) from table;
This stretch: // Also only fetch if never been sent before // HERE SHOULD USE THE BELOW RELATIONSHIP var innerQuery = new Parse.Query(Parse.User); innerQuery.exists(Parse.User); query.matchesQuery(“sentTo”, innerQuery); Could be changed to: // Also only fetch if never been sent before query.notContainedIn(“sentTo”,[Parse.User.current()]) That works.Parse Query
I know this question is about MySQL, but for what it’s worth, count(*) is recommended for Oracle, which goes to show that the answer to this can be database dependent (see comment above from BalusC). Since a lot of databases (MS-SQL, MySQL) have information schema tables that hold various types of metadata, there are bound … Read more
Probably not the most elegant of solutions, and the performance of IN may suffer on larger tables. The nested query gets the minimum Birthyear for each city. Only records who have this Birthyear are matched in the outer query. Ordering by age then limiting to 3 results gets you the 3 oldest people who are … Read more