[#10] Support CASE

This includes:
- CASE abbreviations
- CASE simple
- CASE searched

src/main/java/org/neo4j/sql2cypher/Translator.java

@@ -42,6 +42,7 @@
 import org.jooq.impl.DefaultConfiguration;
 import org.jooq.impl.QOM;
 import org.jooq.impl.QOM.TableAlias;
+import org.neo4j.cypherdsl.core.Case;
 import org.neo4j.cypherdsl.core.Condition;
 import org.neo4j.cypherdsl.core.Cypher;
 import org.neo4j.cypherdsl.core.Expression;
@@ -354,6 +355,42 @@ else if (f instanceof QOM.Nvl<?> e) {
 			return Functions.coalesce(expression(e.$arg1()), expression(e.$arg2()));
 		}
 
+		// https://neo4j.com/docs/cypher-manual/current/syntax/expressions/
+		else if (f instanceof QOM.Nullif<?> e) {
+			return Cypher.caseExpression().when(expression(e.$arg1()).eq(expression(e.$arg2())))
+					.then(Cypher.literalNull()).elseDefault(expression(e.$arg1()));
+		}
+		else if (f instanceof QOM.Nvl2<?> e) {
+			return Cypher.caseExpression().when(expression(e.$arg1()).isNotNull()).then(expression(e.$arg2()))
+					.elseDefault(expression(e.$arg3()));
+		}
+		else if (f instanceof QOM.CaseSimple<?, ?> e) {
+			Case c = Cypher.caseExpression(expression(e.$value()));
+
+			for (var w : e.$when()) {
+				c = c.when(expression(w.$1())).then(expression(w.$2()));
+			}
+
+			if (e.$else() != null) {
+				c = ((Case.CaseEnding) c).elseDefault(expression(e.$else()));
+			}
+
+			return c;
+		}
+		else if (f instanceof QOM.CaseSearched<?> e) {
+			Case c = Cypher.caseExpression();
+
+			for (var w : e.$when()) {
+				c = c.when(condition(w.$1())).then(expression(w.$2()));
+			}
+
+			if (e.$else() != null) {
+				c = ((Case.CaseEnding) c).elseDefault(expression(e.$else()));
+			}
+
+			return c;
+		}
+
 		// Others
 		else if (f instanceof QOM.Cast<?> e) {
 			if (e.$dataType().isString()) {

src/test/resources/expressions.adoc

@@ -109,7 +109,18 @@ The input
 
 [source,sql,id=t6_0,name=select_with_string_functions]
 ----
-SELECT coalesce(1, 2), coalesce(1, 2, 3), nvl(1, 2), cast('1' as boolean), cast(1 as float), cast(1 as double precision), cast(1 as real), cast(1 as tinyint), cast(1 as smallint), cast(1 as int), cast(1 as bigint)
+SELECT
+    coalesce(1, 2),
+    coalesce(1, 2, 3),
+    nvl(1, 2),
+    cast('1' as boolean),
+    cast(1 as float),
+    cast(1 as double precision),
+    cast(1 as real),
+    cast(1 as tinyint),
+    cast(1 as smallint),
+    cast(1 as int),
+    cast(1 as bigint)
 ----
 
 will be transpiled to
@@ -118,3 +129,66 @@ will be transpiled to
 ----
 RETURN coalesce(1, 2), coalesce(1, 2, 3), coalesce(1, 2), toBoolean('1'), toFloat(1), toFloat(1), toFloat(1), toInteger(1), toInteger(1), toInteger(1), toInteger(1)
 ----
+
+
+== Query syntax expressions
+
+See https://neo4j.com/docs/cypher-manual/current/syntax/expressions
+
+=== `CASE` simple
+
+The input
+
+[source,sql,id=t7_0,name=select_with_string_functions]
+----
+SELECT
+    CASE 1 WHEN 2 THEN 3 END,
+    CASE 1 WHEN 2 THEN 3 ELSE 4 END,
+    CASE 1 WHEN 2 THEN 3 WHEN 4 THEN 5 END,
+    CASE 1 WHEN 2 THEN 3 WHEN 4 THEN 5 ELSE 6 END
+----
+
+will be transpiled to
+
+[source,cypher,id=t7_0_expected]
+----
+RETURN CASE 1 WHEN 2 THEN 3 END, CASE 1 WHEN 2 THEN 3 ELSE 4 END, CASE 1 WHEN 2 THEN 3 WHEN 4 THEN 5 END, CASE 1 WHEN 2 THEN 3 WHEN 4 THEN 5 ELSE 6 END
+----
+
+=== `CASE` searched
+
+The input
+
+[source,sql,id=t7_1,name=select_with_string_functions]
+----
+SELECT
+    CASE WHEN 1 = 2 THEN 3 END,
+    CASE WHEN 1 = 2 THEN 3 ELSE 4 END,
+    CASE WHEN 1 = 2 THEN 3 WHEN 4 = 5 THEN 6 END,
+    CASE WHEN 1 = 2 THEN 3 WHEN 4 = 5 THEN 6 ELSE 7 END
+----
+
+will be transpiled to
+
+[source,cypher,id=t7_1_expected]
+----
+RETURN CASE WHEN 1 = 2 THEN 3 END, CASE WHEN 1 = 2 THEN 3 ELSE 4 END, CASE WHEN 1 = 2 THEN 3 WHEN 4 = 5 THEN 6 END, CASE WHEN 1 = 2 THEN 3 WHEN 4 = 5 THEN 6 ELSE 7 END
+----
+
+=== `CASE` abbreviations (which aren't `COALESCE` or `NVL`)
+
+The input
+
+[source,sql,id=t7_2,name=select_with_string_functions]
+----
+SELECT
+    nullif(1, 2),
+    nvl2(1, 2, 3)
+----
+
+will be transpiled to
+
+[source,cypher,id=t7_2_expected]
+----
+RETURN CASE WHEN 1 = 2 THEN NULL ELSE 1 END, CASE WHEN 1 IS NOT NULL THEN 2 ELSE 3 END
+----