From 18117bb7cccbea4e450ea7057da9937950f8c33b Mon Sep 17 00:00:00 2001
From: Tanner Clary <tannerclary@google.com>
Date: Wed, 27 Mar 2024 10:27:31 -0700
Subject: [PATCH] [b/330573524] Prevent IF from treating NULL as FALSE

Tableau offers the IIF function with the signature IIF(bool, val1, val2[, val3]). If bool is TRUE, it returns val1, if it is FALSE, it returns val2, and if it is NULL, it returns val3 if provided, otherwise it returns NULL.

Previously, we translated this behavior by rewriting it as BigQuery's IF. The issue however, is that if bool is NULL, BigQuery defaults to val2 instead of NULL or val3.

This commit corrects for that by wrapping the expression in another IF that checks if bool is NULL. If it is, it returns val3 if specified, otherwise NULL. If bool is not null, it follows normal IF behavior.
---
 connector/tableau/looker-jdbc/dialect.tdd | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/connector/tableau/looker-jdbc/dialect.tdd b/connector/tableau/looker-jdbc/dialect.tdd
index 7136ee4bff4..389a86521dd 100644
--- a/connector/tableau/looker-jdbc/dialect.tdd
+++ b/connector/tableau/looker-jdbc/dialect.tdd
@@ -667,7 +667,8 @@
       <argument type='spatial' />
     </function>
     <function group='logical' name='IIF' return-type='bool'>
-      <formula>IF((%1), (%2), (%3))</formula>
+      <!-- To prevent IF from coercing NULL to FALSE, wrap in another IF that checks for NULL. -->
+      <formula>IF((%1) IS NOT NULL, IF((%1), (%2), (%3)), NULL)</formula>
       <argument type='bool' />
       <argument type='bool' />
       <argument type='bool' />
@@ -687,7 +688,7 @@
       <argument type='real' />
     </function>
     <function group='logical' name='IIF' return-type='int'>
-      <formula>IF((%1), (%2), (%3))</formula>
+      <formula>IF((%1) IS NOT NULL, IF((%1), (%2), (%3)), NULL)</formula>
       <argument type='bool' />
       <argument type='int' />
       <argument type='int' />
@@ -700,7 +701,7 @@
       <argument type='int' />
     </function>
     <function group='logical' name='IIF' return-type='str'>
-      <formula>IF((%1), (%2), (%3))</formula>
+      <formula>IF((%1) IS NOT NULL, IF((%1), (%2), (%3)), NULL)</formula>
       <argument type='bool' />
       <argument type='str' />
       <argument type='str' />
@@ -713,7 +714,7 @@
       <argument type='str' />
     </function>
     <function group='logical' name='IIF' return-type='datetime'>
-      <formula>IF((%1), (%2), (%3))</formula>
+      <formula>IF((%1) IS NOT NULL, IF((%1), (%2), (%3)), NULL)</formula>
       <argument type='bool' />
       <argument type='datetime' />
       <argument type='datetime' />
@@ -726,7 +727,7 @@
       <argument type='datetime' />
     </function>
     <function group='logical' name='IIF' return-type='date'>
-      <formula>IF((%1), (%2), (%3))</formula>
+      <formula>IF((%1) IS NOT NULL, IF((%1), (%2), (%3)), NULL)</formula>
       <argument type='bool' />
       <argument type='date' />
       <argument type='date' />
@@ -739,7 +740,7 @@
       <argument type='date' />
     </function>
     <function group='logical' name='IIF' return-type='spatial'>
-      <formula>IF((%1), (%2), (%3))</formula>
+      <formula>IF((%1) IS NOT NULL, IF((%1), (%2), (%3)), NULL)</formula>
       <argument type='bool' />
       <argument type='spatial' />
       <argument type='spatial' />