Case sql postgres9/8/2023 ![]() ![]() There are two forms of the CASE statement: Simple CASE statement Searched CASE statement Simple CASE statement Syntax: CASE search-expression WHEN expression1, expression2. Here is a proof of concept.īut, honestly, I'd rather avoid the complication and just use the simple query above. PostgreSQL provides you with CASE statements that allow you to execute a block of code conditionally. You want a simple call like this? SELECT * FROM f_tbl_counts_6months(NULL::m6_jul) But do you actually need the pivoted form? OK, you asked for it. Well, you could prepare 12 different row types (that's the range of possible result types for your case) and use a polymorphic function to achieve it. If you really need that, you need a 2-step flow of operation (two round trips to the server): But dynamic column names are not possible for a static SQL query. Your original query produces that information in pivoted form: one month per column. Using standard English month names and 3-letter-abbreviations. Query with LEFT JOIN not returning rows for count of 0.Note, in particular, that it's faster to aggregate first and join later. PostgreSQL: running count of rows for a query 'by minute'.COALESCE makes the count 0 instead of NULL for that case. This way always returns the last 6 months, even if no rows are found at all. Then LEFT JOIN to counts per month from the relevant time range. Introduction to PostgreSQL CASE Each condition is a boolean expression and based on its output the result is chosen. Generating time series between two dates in PostgreSQL.Note how I first build timestamps for the last six months (excluding the current one) with generate_series() in the first subquery mon. Returns one row per month, in chronological order (considering the year, too, though it's not in your output!), and truly dynamic. (I'd rather not use start as column name as that's a keyword in standard SQL - even if allowed in Postgres.) SELECT date_trunc('month', start) AS mon, count(*) AS ctĪND start = c.current_mon - interval '6 mon' Syntax Below is the syntax of the case statement. The case statement is significant in PostgreSQL to formulate the conditional expression we formulate the conditional by using the when and then keyword in PostgreSQL. WHERE fuel_descriptions.The column month seems to be redundant. We can use the case statement in PostgreSQL using a when and a keyword like if and else in other programming languages. LEFT JOIN dailywx ON px_f_weathercell.fid_new_wx_cells = dailywx.location LEFT JOIN f_descriptions ON px_f_weathercell.px_id = f_descriptions.fuel_id WHEN 'SUNNY' then dailywx.hoursabove4k_sunny I'm still recieving null values from the CASE statement, however. This has resulted in 100,000 records returning in approx 5-7 seconds. I've also set an index on px_f_weathercell.fid_new_wx_cells and px_f_weathercell.px_id. I've also used PGTune to set some recommended settings in order to address a situation where the process was disk bound. Both columns are of type double.ĮDIT2: Updated a couple of table names to indicate where columns are coming from. Made the following edit, no getting a column full of nulls when the column desired has numbers (including 0) in it. The error is as follows: ERROR: syntax error at or near "CASE"īonus points: CASE seems slow. ![]() WHERE best_model_fit = 'SUNNY' /* limiting my test case here, clause will be removed later */ INNER JOIN dailywx ON px_f_weathercell.fid_new_wx_cells = dailywx.location INNER JOIN f_descriptions ON px_f_weathercell.px_id = f_descriptions.fuel_id I'm going to guess that my INNER JOIN and CASE statements are back to front, but I'm not sure how to rearrange them without breaking the intent.īasically: Where model_best_fit = SUNNY, then I'd like a new column with name applied_f_model_hours_above4k to have the value from the column hoursabove4k_sunny I'm left joining three tables, and would like to be able to use a case statement to introduce another column that brings across a desired value from one column based on another. I'm a Postgresql newbie, so still struggling a little bit here. ![]()
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