In a previous blog post, we've advertised the use of SQL EXISTS rather than COUNT(*) to check for existence of a value in SQL. I.e. to check if in the Sakila database, actors called WAHLBERG have played in any films, instead of: SELECT count(*) FROM actor a JOIN film_actor fa USING (actor_id) WHERE a.last_name = … Continue reading An Efficient Way to Check for Existence of Multiple Values in SQL
Tag: mysql
Workaround for MySQL’s “can’t specify target table for update in FROM clause” Error
In MySQL, you cannot do this: create table t (i int primary key, j int); insert into t values (1, 1); update t set j = (select max(j) from t) + 1; The UPDATE statement will raise an error as follows: SQL Error [1093] [HY000]: You can't specify target table 't' for update in FROM … Continue reading Workaround for MySQL’s “can’t specify target table for update in FROM clause” Error
The Performance of Various To-Many Nesting Algorithms
It's been a while since jOOQ 3.15 has been released with its revolutionary standard SQL MULTISET emulation feature. A thing that has been long overdue and which I promised on twitter a few times is to run a few benchmarks comparing the performance of various approaches to nesting to-many relationships with jOOQ. This article will … Continue reading The Performance of Various To-Many Nesting Algorithms
Setting the JDBC Statement.setFetchSize() to 1 for Single Row Queries
An interesting hint by Vladimir Sitnikov has made me think about a new benchmark for jOOQ: https://twitter.com/lukaseder/status/1407662449331949568 The benchmark should check whether single row queries should have a JDBC Statement.setFetchSize(1) call made to them by default. The Javadoc of the method says: Gives the JDBC driver a hint as to the number of rows that … Continue reading Setting the JDBC Statement.setFetchSize() to 1 for Single Row Queries
MySQL’s allowMultiQueries flag with JDBC and jOOQ
MySQL's JDBC connector has a security feature called allowMultiQueries, which defaults to false. When turned off, it prevents using a useful, but potentially dangerous feature in MySQL via JDBC: try (Statement s = connection.createStatement()) { try { s.execute("create table t (i int);"); // This doesn't work, by default: s.executeUpdate(""" insert into t values (1); insert … Continue reading MySQL’s allowMultiQueries flag with JDBC and jOOQ
Standard SQL/JSON – The Sobering Parts
It's been almost 1 year now since jOOQ 3.14 was released in October 19, 2020 with SQL/JSON (and SQL/XML) support. Half a year later, we've released jOOQ 3.15 with MULTISET support, which builds on top of these features to offer type-safe nested collections, the way every ORDBMS should implement them. Building (dogfooding) on top of … Continue reading Standard SQL/JSON – The Sobering Parts
jOOQ 3.15’s New Multiset Operator Will Change How You Think About SQL
This is how SQL should have been used all along. They called it The Third Manifesto, ORDBMS, or other things. Regrettably, it never really took off. Because most vendors didn't adopt it. And those who did, didn't agree on syntax. But this is about to change. Thanks to the now ubiquitous SQL/JSON support (which jOOQ … Continue reading jOOQ 3.15’s New Multiset Operator Will Change How You Think About SQL
Having “constant” columns in foreign keys
I was asked a very interesting question on Twitter just now: https://twitter.com/connolly_s/status/1303957373107818497 Can we have "constant" foreign key columns in (PostgreSQL) tables? Luckily, yes, we can. Using a nice standard feature that is "computed columns" or "generated columns" Sometimes, you cannot completely normalise your schema for whatever reason. There may be a case where you … Continue reading Having “constant” columns in foreign keys
Using SQL Server FOR XML and FOR JSON Syntax on Other RDBMS With jOOQ
SQL Server supports transforming flat tabular SQL result sets into hierarchical structures by convention using the convenient FOR XML or FOR JSON syntaxes. This is really convenient and less verbose than the standard SQL/XML or SQL/JSON APIs - although the standard ones are more powerful. In this blog post, I'd like to show a few … Continue reading Using SQL Server FOR XML and FOR JSON Syntax on Other RDBMS With jOOQ
How to Map MySQL’s TINYINT(1) to Boolean in jOOQ
MySQL 8 does not yet support the BOOLEAN type as specified in the SQL standard. There is a DDL "type" called BOOL, which is just an alias for TINYINT: create table t(b bool); select table_name, column_name, data_type, column_type from information_schema.columns where table_name = 't'; The above produces: TABLE_NAME|COLUMN_NAME|DATA_TYPE|COLUMN_TYPE| ----------|-----------|---------|-----------| t |b |tinyint |tinyint(1) | Notice … Continue reading How to Map MySQL’s TINYINT(1) to Boolean in jOOQ