This is called a correlated update UPDATE table1 t1 SET (name, desc) = (SELECT t2.name, t2.desc FROM table2 t2 WHERE t1.id = t2.id) WHERE EXISTS ( SELECT 1 FROM table2 t2 WHERE t1.id = t2.id ) Assuming the join results in a key-preserved view, you could also UPDATE (SELECT t1.id, t1.name name1, t1.desc desc1, t2.name … Read more
Update: SQLite 2021-03-12 (3.35.0) now supports DROP COLUMN. From: http://www.sqlite.org/faq.html: (11) How do I add or delete columns from an existing table in SQLite. SQLite has limited ALTER TABLE support that you can use to add a column to the end of a table or to change the name of a table. If you want … Read more
Here’s how I’d do it – For Schemas (or Databases – they are synonyms): SELECT default_character_set_name FROM information_schema.SCHEMATA WHERE schema_name = “mydatabasename”; For Tables: SELECT CCSA.character_set_name FROM information_schema.`TABLES` T, information_schema.`COLLATION_CHARACTER_SET_APPLICABILITY` CCSA WHERE CCSA.collation_name = T.table_collation AND T.table_schema = “mydatabasename” AND T.table_name = “tablename”; For Columns: SELECT character_set_name FROM information_schema.`COLUMNS` WHERE table_schema = “mydatabasename” AND table_name … Read more
Writing deadlock-proof code is really hard. Even when you access the tables in the same order you may still get deadlocks [1]. I wrote a post on my blog that elaborates through some approaches that will help you avoid and resolve deadlock situations. If you want to ensure two statements/transactions will never deadlock you may … Read more
How much writing vs. reading of this table(s) do you expect? I’ve used a single audit table, with columns for Table, Column, OldValue, NewValue, User, and ChangeDateTime – generic enough to work with any other changes in the DB, and while a LOT of data got written to that table, reports on that data were … Read more
In Mysql there is a cheap trick to do this: mysql> select ~0; +———————-+ | ~0 | +———————-+ | 18446744073709551615 | +———————-+ the tilde is the bitwise negation. The resulting value is a bigint. See: http://dev.mysql.com/doc/refman/5.1/en/bit-functions.html#operator_bitwise-invert For the other integer flavours, you can use the right bitshift operator >> like so: SELECT ~0 as max_bigint_unsigned … Read more
Update: This article in my blog summarizes both my answer and my comments to another answers, and shows actual execution plans: IN vs. JOIN vs. EXISTS SELECT * FROM a WHERE a.c IN (SELECT d FROM b) SELECT a.* FROM a JOIN b ON a.c = b.d These queries are not equivalent. They can yield … Read more
With cte as ( select top(1) shipfirtsname From ShipBillInfo where CustomerId=’134′ order by OredrGUID desc) Update cte set shipfirstname=”abc”;
Since Cassandra 3.4 (3.5 recommended), LIKE queries can be achieved using a SSTable Attached Secondary Index (SASI). For example: CREATE TABLE cycling.cyclist_name ( id UUID PRIMARY KEY, lastname text, firstname text ); Creating the SASI as follows: CREATE CUSTOM INDEX fn_prefix ON cyclist_name (firstname) USING ‘org.apache.cassandra.index.sasi.SASIIndex’; Then a prefix LIKE query is working: SELECT * … Read more
Union will be faster, as it simply passes the first SELECT statement, and then parses the second SELECT statement and adds the results to the end of the output table. The Join will go through each row of both tables, finding matches in the other table therefore needing a lot more processing due to searching … Read more