#Postgres if in select how to#
#Postgres if in select code#

If not found then raise notice 'The film % could not be found',Įlse raise notice 'The film title is %', selected_film.title The following flowchart illustrates the if else statement. The if then else statement executes the statements in the if branch if the condition evaluates to true otherwise, it executes the statements in the else branch.

#Postgres if in select code#

The following illustrates the syntax of the if-then-else statement: if condition thenĮND if Code language: PostgreSQL SQL dialect and PL/pgSQL ( pgsql ) If you change the value of the input_film_id variable to some value that exists in the film table like 100, you will not see any message. ERROR: The film 0 could not be found Code language: Shell Session ( shell ) We used the if statement to check if the film with id (0) exists and raise a notice if it does not. If the select into statement sets the found variable if a row is assigned or false if no row is returned. The found is a global variable that is available in PL/pgSQL procedure language. In this example, we selected a film by a specific film id ( 0). If not found then raise notic e'The film % could not be found',Įnd $$ Code language: PostgreSQL SQL dialect and PL/pgSQL ( pgsql ) The following flowchart illustrates the simple if statement. When an if statement is placed inside another if statement, it is called a nested-if statement.

It can be any valid statement, even another if statement. The statements can be one or more statements that will be executed if the condition is true. The condition is a boolean expression that evaluates to true or false. If the condition evaluates to false, the control is passed to the next statement after the END if part. The if statement executes statements if a condition is true. The following illustrates the simplest form of the if statement: if condition thenĮnd if Code language: PostgreSQL SQL dialect and PL/pgSQL ( pgsql ) PL/pgSQL provides you with three forms of the if statements. The if statement determines which statements to execute based on the result of a boolean expression.

#Postgres if in select how to#

However, I expect few people will need to support those old unsupported versions–9.3 was released in 2013, and 9.2 supported ended in 2017.Summary: in this tutorial, you will learn how to use the PL/pgSQL if statements to execute a command based on a specific condition. However, I would not expect it to work in 9.2 or earlier – the -> operator was added in 9.3, and the JSON type and row_to_json function was added in 9.2. (Obviously this approach will not work in Postgres versions which are too old to have the necessary JSON support – I have tested it works in Postgres 9.4 while I haven't tested it in Postgres 9.3, it probably works there. (If your column is of some other type, use the appropriate cast for the type of your column.) Then, ::boolean converts the string value true/ false back into a PostgreSQL boolean value. Next, ->'relispartition' selects the value of the relispartition JSON object key as text, which will be the same as the value of the relispartition column if there is no such key in the JSON, the result of that will be NULL. What this is doing, is row_to_json(c) turns all the data of the row into JSON. You could make it return false instead of NULL in pre-10 versions by doing COALESCE((row_to_json(c)->'relispartition')::boolean,false). If you try running that, you will find on PostgreSQL 10+ the relispartition column is returned as true/ false, whereas in pre-10 versions it is NULL. (row_to_json(c)->'relispartition')::boolean AS relispartition The core SQL language does not have any facility to conditionally select a column, but it is achievable in PostgreSQL using the row_to_json function, as follows: SELECT c.relname, c.relkind, However, suppose you don't want to do that, you want to have a single query which works on both versions – in other words, you want to conditionally select the relispartition column if it exists. However, if you try to run the same query on PostgreSQL 9.6 or earlier, it will fail since the relispartition column does not exist on the pg_class table prior to PostgreSQL 10.Īn obvious solution would be to dynamically generate the SQL based on a condition, or have two different versions of the SQL. In PostgreSQL 10+, that will show you the names of all the tables in public schema, including whether they are partitioned and if so whether the table is the partitioned table or one of the partitions of it.

Consider the following SQL query: SELECT c.relname, c.relkind, c.relispartitionĬ.relnamespace=(SELECT oid FROM pg_namespace WHERE nspname='public') It is possible to achieve this in PostgreSQL using JSON.