In case no expression evaluates to true, the case statement will execute the the else section. Once it finds an expression that evaluates to true, the case statement executes the corresponding when section and immediately stops searching for the remaining expressions. In this syntax, the case statement evaluates the boolean expressions sequentially from top to bottom until it finds an expression that evaluates to true The following syntax shows syntax of the searched case statement: case when boolean-expression -1 thenĮnd case Code language: PostgreSQL SQL dialect and PL/pgSQL ( pgsql ) The following flowchart illustrates the simple case statement in this example: In case the price is not 0.99, 2.99 or 4.99, the case statement assigns the film the price segment as unspecified. Based on the rental rate, it assigns a price segment to the film that can be mass, mainstream, or high end. This example first selects the film with id 100. Output: NOTICE: High End Code language: HTTP ( http ) assign the price segment if found then case rateĮnd $$ Code language: PostgreSQL SQL dialect and PL/pgSQL ( pgsql ) do $$ declareīegin - get the rental rate select rental_rate into rate The following is an example of the simple case statement. If the result of the search-expression does not match expression in the when sections and the else section does not exist, the case statement will raise a case_not_found exception. If the case statement cannot find any match, it will execute the else section. Also, it stops comparing the result of the search-expression with the remaining expressions. If the case statement finds a match, it will execute the corresponding when section. The case statement compares the result of the search-expression with the expression in each when branch using equal operator ( =) from top to bottom. The search-expression is an expression that evaluates to a result. When expression_1 then when-statementsĮND case Code language: PostgreSQL SQL dialect and PL/pgSQL ( pgsql ) Let’s start with the syntax of the simple case statement: case search-expression The case expression evaluates to a value while the case statement selects a section to execute based on condition. Notice that you should not confuse about the case statement and case expression. The case statement selects a when section to execute from a list of when sections based on a condition. It still feels wrong somehow.Summary: in this tutorial, you will learn about the PL/pgSQL case that executes statements based on a certain condition.īesides the if statement, PostgreSQL provides you with case statements that allow you to execute a block of code based on a condition. One way to do this is, maybe try creating an expression index with function being said case statement? create index fact_sales_case on fact_sales ((case I would do "explain" with and without case statement and compare query plans. This will prevent any indexes or histogram optimization to be used on that particular column which is important. Ok, so same case statement is appearing in both group by and order by. It's like building a road based on where a driverless truck is going. In which case you're designing your database to suit my other gripe - the query generator. That of course assumes that your query generator can be told to use the mview instead. Then create a view that selects from the materialized view or denormalized table. If a query like this is run often enough, I would suggest that a materialized view be created, or a table with triggers to store company_code and location_code in the same row as the fact information. In PostgreSQL, that means a BitmapAnd combination of several indexes, tricky to accomplish and it wouldn't apply to this query because there's no filtration of the Fact table other than the existence of reference rows in the two dimensions.existence which is guaranteed by the model.so no filtration whatsoever.ĭata Warehouse applications should feel free to denormalize data to suit reporting needs, provided they keep the denormalized data consistent with the rest of the DW (obviously the whole DW is a little behind the authoritative data source, I'm saying the DW just needs to be consistent with itself). Oracle gets around this with "bitmap join" indexes, but building those are incredibly slow.įact/Dim queries are very heavily reliant on the the query optimizer being able to see the "star join". Everything has to go through synthetic keys. Neither of which is the fault of the poster, obviously.įact/Dimension seems almost designed to foil the ability to put useful indexes on the Fact table. This post demonstrates two of my biggest complaints in the RDBMS world: query generators and the Kimball Fact/Dimension model.
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