SQLite 3.39.0 release supports right external connection and all external connection

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SQLite The development team in 2022 year 06 month 25 Date issued SQLite 3.39.0 edition . The biggest update of this version is to support RIGHT OUTER JOIN and FULL OUTER JOIN, This paper gives you an analysis one by one .

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Right outer connection and all outer connection

all the time ,SQLite Don't support Right outer connection and all outer connection ,SQLite 3.39.0 Finally made up for this defect . thus ,SQLite Provides SQL All in the standard JOIN The way ,MySQL We need gas .

Let's take a simple example ：

sqlite> select sqlite_version();
3.39.0
sqlite> create table t1(id int);
sqlite> insert into t1 values(1),(2),(3);
sqlite> create table t2(id int, name text);
sqlite> insert into t2 values(1, 'one'),(4, 'four');
sqlite> select * from t1 left join t2 on t1.id=t2.id;
1|1|one
2||
3||
sqlite> select * from t2 right join t1 on t1.id=t2.id;
1|one|1
||2
||3
sqlite> select * from t1 full join t2 on t1.id=t2.id;
1|1|one
2||
3||
|4|four

IS [NOT] DISTINCT FROM

SQLite 3.39.0 Two new binary comparison operators have also been added ：IS NOT DISTINCT FROM and IS DISTINCT FROM.

IS NOT DISTINCT FROM Equivalent to IS Operator , They are all related to = Operators are similar to , But support NULL Comparison of values . for example ：

sqlite> select 1=1, 1 IS 1, 1 IS NOT DISTINCT FROM 1;
1|1|1
sqlite> select NULL=NULL, NULL IS NULL, NULL IS NOT DISTINCT FROM NULL;
|1|1

A similar ,IS DISTINCT FROM Equivalent to IS NOT Operator .

Two new operators and SQL Standards and PostgreSQL Achieve compatibility .

C Interface enhancement

Interface sqlite3_vtab_distinct() Added a return code （3）, Indicates that the query uses DISTINCT as well as ORDER BY Clause .

Added a new interface sqlite3_db_name(), Used to return the database name in the database connection .

Other enhancements

UNIX The operating system interface will resolve all symbolic links in the file name before the file is opened , To create a standard name for the database .

Delay materialization of views , It doesn't materialize until it's really needed , So as to avoid unnecessary work .

Can be used in any aggregate query HAVING Clause , Even if there is no GROUP BY Clause . In the previous version ,HAVING Clause must be consistent with GROUP BY Clause is used together , Not alone .

A lot of Micro optimization bring CPU The overall cycle is reduced by about 2.3%.