![]() If stinationhost is NULL, the row will always show up as typeB, because NULL NULL is not TRUE in SQL. Learn more about PostgreSQL in the Xojo Dev Center. WITH subquery AS (.) SELECT CASE WHEN EXISTS (SELECT 1 FROM subquery WHERE subquery.host stinationhost) THEN 'typeA' ELSE 'typeB' END FROM tableb With queries like that, you have to take care of NULL values. If you use a tool’s UI to create a table and have a habit of typing in mixed case, the tool might generate SQL (or even the table itself) for you using quotes, which as you can see could mess you up later. Obviously that can start to become a bit of a pain, so the moral of the story is don’t use quotes when creating tables or writing SQL queries so that everything is created as lowercase and things will work like you probably expect. You’ll especially want to pay attention to any tools you use to create SQL for you. To avoid this error you instead have to write the SQL with quotes like this: SELECT "FullName" FROM "Person" The condition of a WHEN clause must return a. This is because PostgreSQL is converting “Person” to “person”, but there is no table called “person”. The CASE, WHEN, THEN, and ELSE keywords are somewhat similar to the if-then-else logic in programming languages. ![]() Now what happens if you try to run a query with a table called “Person”? Well, using SQL like this: SELECT FullName FROM Person If this is not the case in your data source, consider passing a coalesce function to the. This means you’ll get a table called “Person” with two columns called “FullName” and “Address”. Asserts that a valid SQL expression is true for all records. In the last example, the names are in quotes so their case is maintained. In the first two examples, you get a table called “person” with two columns called “fullname” and “address”. That may not be obvious in the second example since the names are not lowercase, but remember that PostgreSQL converts your SQL to lowercase for you. PostgreSQL provides two forms or types of a case statement first is a general form case statement, and the second is a simple form of the case statement. For example, consider these SQL CREATE statements: CREATE TABLE person (fullname VARCHAR(100), address VARCHAR(100)) CREATE TABLE Person (FullName VARCHAR(100), Address VARCHAR(100)) CREATE TABLE "Person" ("FullName" VARCHAR(100), "Address" VARCHAR(100)) PostgreSQL case statement is the same as the if-else statement defined in other languages like C and C++. That is nice if you happen to like to write your queries with mixed casing.īut you’ll start to run into a problem if you’ve actually created the table with case-sensitive names, which happens when you use quotes around the names. in sql SELECT StoreName, TxnDate, CASE WHEN Sales > 1000 THEN Good Day WHEN Sales > 500 THEN OK Day ELSE Bad Day END Sales Status FROM. ![]() This gets converted to: SELECT fullname FROM person So take a look at this SQL: SELECT FullName FROM Person What it actually does is convert your SQL to lowercase by default. Sometimes you hear that PostgreSQL is case-insensitive, but it isn’t really. You can add multiple WHEN statements.I’ve ran into PostgreSQL case sensitivity myself before and I’ve seen it come up on the forums, so I thought it might be a good thing to bring up here. ![]() Remember, the END at the end of the CASE WHEN expression is important. This is how you can do it − SELECT name, CASE WHEN perc_marks >= 40 THEN 'PASS' ELSE 'FAIL' END Now, if the student has scored above 40 marks, we want to print ‘PASS’ against that student’s name, otherwise ‘FAIL’. If you have table marks containing percentage marks of a student, and you want to find out whether the students have passed or failed. The equivalent in PostgreSQL is CASE WHEN. If you are a programmer, you may be very familiar with IF-ELSE statements.
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