Add support for PostgreSQL STRING_AGG function. Patch by Fred Aquiles.

h2/src/docsrc/html/changelog.html

@@ -59,6 +59,7 @@ Change Log
     throw an exception.
 </li><li>Fix bug in MVStore when creating lots of temporary tables, where we could run out of
     transaction IDs.
+</li><li>Add support for PostgreSQL STRING_AGG function. Patch by Fred Aquiles.    
 </li></ul>
 
 <h2>Version 1.4.186 Beta (2015-03-02)</h2>

h2/src/main/org/h2/command/Parser.java

@@ -2270,7 +2270,7 @@ public class Parser {
         }
     }
 
-    private Expression readAggregate(int aggregateType) {
+    private Expression readAggregate(int aggregateType, String aggregateName) {
         if (currentSelect == null) {
             throw getSyntaxError();
         }
@@ -2293,16 +2293,26 @@ public class Parser {
                 }
             }
         } else if (aggregateType == Aggregate.GROUP_CONCAT) {
+            Aggregate agg = null;
+            if (equalsToken("GROUP_CONCAT", aggregateName)) {
                 boolean distinct = readIf("DISTINCT");
-            Aggregate agg = new Aggregate(Aggregate.GROUP_CONCAT,
+                agg = new Aggregate(Aggregate.GROUP_CONCAT,
                     readExpression(), currentSelect, distinct);
                 if (readIf("ORDER")) {
                     read("BY");
                     agg.setGroupConcatOrder(parseSimpleOrderList());
                 }
+                
                 if (readIf("SEPARATOR")) {
                     agg.setGroupConcatSeparator(readExpression());
                 }
+            } else if (equalsToken("STRING_AGG", aggregateName)) {
+                // PostgreSQL compatibility: string_agg(expression, delimiter)
+                agg = new Aggregate(Aggregate.GROUP_CONCAT,
+                    readExpression(), currentSelect, false);
+                read(",");
+                agg.setGroupConcatSeparator(readExpression());
+            }
             r = agg;
         } else {
             boolean distinct = readIf("DISTINCT");
@@ -2382,7 +2392,7 @@ public class Parser {
         }
         int agg = getAggregateType(name);
         if (agg >= 0) {
-            return readAggregate(agg);
+            return readAggregate(agg, name);
         }
         Function function = Function.getFunction(database, name);
         if (function == null) {

h2/src/main/org/h2/expression/Aggregate.java

@@ -163,6 +163,8 @@ public class Aggregate extends Expression {
         addAggregate("MAX", MAX);
         addAggregate("AVG", AVG);
         addAggregate("GROUP_CONCAT", GROUP_CONCAT);
+        // PostgreSQL compatibility: string_agg(expression, delimiter)
+        addAggregate("STRING_AGG", GROUP_CONCAT);
         addAggregate("STDDEV_SAMP", STDDEV_SAMP);
         addAggregate("STDDEV", STDDEV_SAMP);
         addAggregate("STDDEV_POP", STDDEV_POP);

h2/src/test/org/h2/test/testScript.sql

@@ -8188,6 +8188,12 @@ SELECT GROUP_CONCAT(ID ORDER BY ID) FROM TEST;
 > 1,2,3,4,5,6,7,8,9
 > rows (ordered): 1
 
+SELECT STRING_AGG(ID,';') FROM TEST;
+> GROUP_CONCAT(ID SEPARATOR ';')
+> ------------------------------
+> 1;2;3;4;5;6;7;8;9
+> rows: 1
+
 SELECT DISTINCT NAME FROM TEST;
 > NAME
 > --------