{"id":11035,"date":"2018-03-20T16:58:37","date_gmt":"2018-03-20T15:58:37","guid":{"rendered":"https:\/\/www.dbi-services.com\/blog\/postgresql-11-procedures-and-transaction-control\/"},"modified":"2018-03-20T16:58:37","modified_gmt":"2018-03-20T15:58:37","slug":"postgresql-11-procedures-and-transaction-control","status":"publish","type":"post","link":"https:\/\/www.dbi-services.com\/blog\/postgresql-11-procedures-and-transaction-control\/","title":{"rendered":"PostgreSQL 11: Procedures and transaction control"},"content":{"rendered":"

Up to PostgreSQL 10 it was not possible to create procedures in PostgreSQL. Of course you can create functions which do not return anything but the possibility to create a procedure was not there. That will probably change in PostgreSQL 11 when nothing happens which will lead to the removal of that commit<\/a>. On top of that there was another commit<\/a> which enables transaction control inside procedures which can be quite interesting. Lets see how that works.<\/p>\n

<\/p>\n

Up to PostgreSQL 10 the only choice to have something like a procedure is to create a function returning void:<\/p>\n

\npostgres=# select version();\n                                                          version                                                           \n----------------------------------------------------------------------------------------------------------------------------\n PostgreSQL 10.0 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 4.8.5 20150623 (Red Hat 4.8.5-16), 64-bit\n(1 row)\n\npostgres=# CREATE FUNCTION dummy_func (id int) RETURNS VOID AS $$\npostgres$# DECLARE \npostgres$# BEGIN\npostgres$#   RAISE NOTICE 'id is %', id;\npostgres$# END;\npostgres$# $$  LANGUAGE plpgsql;\nCREATE FUNCTION\npostgres=# set client_min_messages = 'NOTICE';\nSET\npostgres=# select dummy_func(1);\nNOTICE:  id is 1\n dummy_func \n------------\n \n(1 row)\n<\/pre>\n
When you tried to do something like this it was not possible:<\/p>\n
\npostgres=# CREATE PROCEDURE dummy_proc (id int) AS $$\npostgres$# DECLARE \npostgres$# BEGIN\npostgres$#   raise notice 'id is %', id;\npostgres$# END;\npostgres$# $$  LANGUAGE plpgsql;\nERROR:  syntax error at or near \"PROCEDURE\"\nLINE 1: CREATE PROCEDURE dummy_proc (id int) AS $$\n<\/pre>\n
But now in the PostgreSQL development version you can do it (CREATE PROCEDURE<\/a>):<\/p>\n
\npostgres=# select version();\n                                                  version                                                   \n------------------------------------------------------------------------------------------------------------\n PostgreSQL 11devel on x86_64-pc-linux-gnu, compiled by gcc (GCC) 4.8.5 20150623 (Red Hat 4.8.5-16), 64-bit\n(1 row)\n\npostgres=# CREATE PROCEDURE dummy_proc (id int) AS $$\npostgres$# DECLARE \npostgres$# BEGIN\npostgres$#   raise notice 'id is %', id;\npostgres$# END;\npostgres$# $$  LANGUAGE plpgsql;\nCREATE PROCEDURE\npostgres=# call dummy_proc(1);\nNOTICE:  id is 1\nCALL\n<\/pre>\n
Also notice that you need to use call<\/a> to execute a procedure. Using select as you would do it for a function will not work:<\/p>\n
\npostgres=# select dummy_proc(1);\nERROR:  dummy_proc(integer) is a procedure\nLINE 1: select dummy_proc(1);\n               ^\nHINT:  To call a procedure, use CALL.\n<\/pre>\n
On top of the commit which introduced procedures there was another one (see the beginning of this post) which introduced transaction control for procedures<\/a>. As the name implies this can be useful when you want to control transactions inside the procedure, e.g.:<\/p>\n
\npostgres=# create table t1 ( a int primary key );\nCREATE TABLE\npostgres=# CREATE OR REPLACE PROCEDURE dummy_proc2 (id int) AS $$\npostgres$# DECLARE \npostgres$#   l_id int := id;\npostgres$# BEGIN\npostgres$#   raise notice 'id is %', l_id;\npostgres$#   insert into t1 (a) values (l_id);\npostgres$#   commit;\npostgres$#   l_id := l_id + 1;\npostgres$#   raise notice 'id is %', l_id;\npostgres$#   insert into t1 (a) values (l_id);\npostgres$#   commit;\npostgres$#   raise notice 'id is %', l_id;\npostgres$#   insert into t1 (a) values (l_id);\npostgres$# END;\npostgres$# $$  LANGUAGE plpgsql;\n<\/pre>\n
When you execute this it will violate the primary key with the third insert:<\/p>\n
\npostgres=# call dummy_proc2(1);\nNOTICE:  id is 1\nNOTICE:  id is 2\nNOTICE:  id is 2\nERROR:  duplicate key value violates unique constraint \"t1_pkey\"\nDETAIL:  Key (a)=(2) already exists.\nCONTEXT:  SQL statement \"insert into t1 (a) values (l_id)\"\nPL\/pgSQL function dummy_proc2(integer) line 13 at SQL statement\n<\/pre>\n
… but because we can now commit (or rollback) in between we did not lose all the records:<\/p>\n
\npostgres=# select * from t1;\n a \n---\n 1\n 2\n(2 rows)\n<\/pre>\n
Trying to do the same with a function in PostgreSQL 10 will not work:<\/p>\n
\npostgres=# create table t1 ( a int primary key );\nCREATE TABLE\npostgres=# CREATE FUNCTION dummy_func2 (id int) RETURNS VOID AS $$\npostgres$# DECLARE \npostgres$#   l_id int := id;\npostgres$# BEGIN\npostgres$#   raise notice 'id is %', l_id;\npostgres$#   insert into t1 (a) values (l_id);\npostgres$#   commit;\npostgres$#   l_id := l_id + 1;\npostgres$#   raise notice 'id is %', l_id;\npostgres$#   insert into t1 (a) values (l_id);\npostgres$#   commit;\npostgres$#   raise notice 'id is %', l_id;\npostgres$#   insert into t1 (a) values (l_id);\npostgres$# END;\npostgres$# $$  LANGUAGE plpgsql;\nCREATE FUNCTION\npostgres=# select dummy_func2(1);\nNOTICE:  id is 1\nERROR:  cannot begin\/end transactions in PL\/pgSQL\nHINT:  Use a BEGIN block with an EXCEPTION clause instead.\nCONTEXT:  PL\/pgSQL function dummy_func2(integer) line 7 at SQL statement\npostgres=# select * from t1;\n a \n---\n(0 rows)\n<\/pre>\n
Nice features …<\/p>\n","protected":false},"excerpt":{"rendered":"
Up to PostgreSQL 10 it was not possible to create procedures in PostgreSQL. Of course you can create functions which do not return anything but the possibility to create a procedure was not there. That will probably change in PostgreSQL 11 when nothing happens which will lead to the removal of that commit. On top […]<\/p>\n","protected":false},"author":28,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[229],"tags":[586],"type_dbi":[],"class_list":["post-11035","post","type-post","status-publish","format-standard","hentry","category-database-administration-monitoring","tag-postegresql"],"acf":[],"yoast_head":"\nPostgreSQL 11: Procedures and transaction control - dbi Blog<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.dbi-services.com\/blog\/postgresql-11-procedures-and-transaction-control\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"PostgreSQL 11: Procedures and transaction control\" \/>\n<meta property=\"og:description\" content=\"Up to PostgreSQL 10 it was not possible to create procedures in PostgreSQL. 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