Is
IF(CS2_PDM_D_Mini IS NULL,0,CS2_PDM_D_Mini)
equal
COALESCE(CS2_PDM_D_Mini),0)
Because of Postgres doesn't understand IF, I have plenty of MySQL IF statements into one SQL query, to transmute into a thing that PostgreSQL accepts
If you want to mock up Mysql IF format, use CASE WHEN THEN END, like here:
t=# select case when CS2_PDM_D_Mini is null then 0 else CS2_PDM_D_Mini end ;
Check out docs for both CASE and COALESCE:
The COALESCE function returns the first of its arguments that is not
null
IF is pl/PgSql statement
Related
I am new to COALESCE function in REDSHIFT. I ran below four queries in mysql and Redshift.
1st and 2nd query executed as expected in both mysql and redshift. But for 3rd and 4th query I am getting two different results in mysql and Redshift. How does this behave?
select COALESCE(null,null,1) -> 1
select COALESCE(null,null,'John') -> 1
select COALESCE(null,null,1,'John') -> (Redshift : error , mysql:1)
select COALESCE(null,null,'John',1) -> (Redshift: error, mysql:John)
Also this query should give error in mysql but it has succeeded
Any help is appreciated
Amazon Redshift Database Developer Guide claims:
An NVL expression is identical to a COALESCE expression. NVL and
COALESCE are synonyms.
Syntax
NVL | COALESCE ( expression, expression, ... )
An NVL or COALESCE expression returns the value of the first expression
in the list that is not null. If all expressions are null, the result
is null. When a non-null value is found, the remaining expressions in
the list are not evaluated.
This type of expression is useful when you want to return a backup
value for something when the preferred value is missing or null. For
example, a query might return one of three phone numbers (cell, home,
or work, in that order), whichever is found first in the table (not
null).
If you obtain the error this may mean that the returned value datatype do not match the datatype of recordset field or any another structure which must accept the returned value.
PS. Will you show error messages?
Though it is not written in the documentation, but coalesce works on the compatible data types. Integer and varchar cannot be compared.
The error becomes more evident when you provide column name instead of hard-code values. Try executing this:
select coalesce(integer_column, varchar_column) from a_table;
You would get an error saying something like this:
coalesce types integer and varchar cannot be matched.
Please, I do not understand why it is not working:
SET #key = (SELECT customer.key_stamp FROM customer WHERE customer.key_stamp = "0000");
CASE WHEN (#key > 0) THEN
INSERT INTO transaction
(transaction.to, transaction.key, transaction.type, transaction.cost_bitcoin, transaction.quantity)
VALUES ("0000", "f5rwsd", 2, 0.0075,
(500000 +
(
(SELECT bonus.amount
FROM bonus
WHERE 500000 BETWEEN bonus.min_quantity AND bonus.max_quantity
) / 500000
) * 100))
END;
I tried the CASE STATEMENT, but it still does not work, and i can't understand the issue.
Please help.
CASE is not a valid MySQL statement. (It's not a valid statement outside the context of a MySQL stored program.)
"Why it is not work"... is because it's not valid SQL.
A CASE expression can be used in a SQL statement where an expression is allowed. (In SQL, an expression returns a value of a particular datatype.)
As an example of using a CASE expression in a SQL statement, something like this:
SELECT CASE WHEN #key > 0 THEN 'somevalue' ELSE 'othervalue' END AS foo
in fact now i use just an sql functions, and it work now, all work, switch case mysql, if else statement mysql, and loops too, like while do, or LOOP ITERATE, all work, just need use it in sql functions, or sql procedure.
I want to run a case statement that runs different SELECT Statements Based on a condition in Spark SQL but not able to get the Syntax Right .
My SQL statement looks like this
registerTable(sql="SELECT CASE WHEN typedKeyword > '' THEN (SELECT * FROM `temp.sdf0` WHERE originalKeyword > ''AND keyword > '' AND deviceType = 'devicetype' ) ELSE (SELECT * FROM `temp.tes` WHERE originalKeyword > ''AND keyword > '' ) END ",alias="temp.test")
I don't know if CASE statement is supported in spark SQL so How can one achieve this
I've worked in nearly a dozen SQL and SQL-like dialects and I've never seen syntax like that. It looks like there's a core misunderstanding of what SQL clauses are supposed to do what.
The SELECT clause is for describing a projection of scalar elements. In many dialects you can issue subqueries - sometimes even correlated subqueries - in this clause, but you always must apply an operator that converts the result into a scalar value. For example:
SELECT (CASE WHEN EXISTS (SELECT foo FROM tbl) THEN 1 ELSE 0 END)
Here the "EXISTS" operator converts the uncorrelated subquery into a scalar boolean, so it's legal.
The lack of a FROM clause in the top level query is also a big red flag. It, or some analogue like Oracle's "dual", is legal in about half of the dialects I've seen, but if what you're trying to do is dynamically switch between two queries, you're almost certainly doing it wrong. juergen is right - what you probably meant to do is use 2 different queries.
Just wondering, how this query will be handled by MySQL, will sum() calculated twice if sum(credits) != NULL or does MySQL has optimization in place for such queries.
select if(sum(credits)=NULL, 0, sum(credits)) from ......
Thanks
If won't work. The first condition is always false. The correct way to compare to NULL is IS NULL, not =.
Just use this construct:
select coalesce(sum(credits), 0)
Using IF
SELECT IF(sum(credits) IS NULL, 0 ,sum(credits)) .....
IF(expr1,expr2,expr3)
If expr1 is TRUE (expr1 <> 0 and expr1 <> NULL) then IF() returns expr2; otherwise it returns expr3. IF() returns a numeric or string value, depending on the context in which it is used
Using IFNULL
SELECT IFNULL(sum(credits), 0) .....
Using COALESCE
SELECT COALESCE(sum(credits), 0) .....
Refer : MySQL Control Flow Functions
This is something we shouldn't worry about. With SQL we tell the DBMS what to do, not how to do it.
It is very, very likely that the DBMS will compute sum(credits) only once. It would seem rather stupid if not. However, this is not dictated by the SQL standard, so the DBMS programmers are free to choose how to code this. They could write the DBMS such that sum(credits) is computed twice. We cannot know whether they did or not, but as mentioned it is not likely and we shouldn't worry about it either.
I am using MySQL 5.0'
I want display user defined column when there is no data in select statement.
Example,
i want to display 'No records found' when there is no data in select statement.
You should look at the MySQL function ISNULL() for that (and then use it in your SELECT statement).
If the value is not necessarily NULL than you can use the IF() function.