extended support Postgres' Extract( field FROM source) where field is a String instead of a Keyword (#1591)

Fixes #1582
Amend the ExtractExpression
Add Test case for issue #1582
Amend the README

Author: manticore-projects

README.md

@@ -73,6 +73,7 @@ Additionally, we have fixed many errors and improved the code quality and the te
 * support table option **character set** and **index** options
 * support Postgresql optional **TABLE** in **TRUNCATE**
 * support for `ANALYZE mytable`
+* extended support Postgres' `Extract( field FROM source)` where `field` is a String instead of a Keyword
 
 
 ## Building from the sources

src/main/jjtree/net/sf/jsqlparser/parser/JSqlParserCC.jjt

@@ -4410,13 +4410,14 @@ WindowOffset WindowOffset():
 ExtractExpression ExtractExpression() :
 {
     ExtractExpression retval = new ExtractExpression();
-    String token = null;
+    String fieldName = null;
+    Token token = null;
     Expression expr = null;
 }
 {
     <K_EXTRACT>
     "("
-        token=RelObjectName() { retval.setName(token); }
+        ( fieldName=RelObjectName() { retval.setName(fieldName); } | token=<S_CHAR_LITERAL> { retval.setName(token.image); } )
         <K_FROM>
         expr=SimpleExpression() { retval.setExpression(expr); }
     ")"

src/test/java/net/sf/jsqlparser/statement/select/PostgresTest.java

@@ -0,0 +1,35 @@
+package net.sf.jsqlparser.statement.select;
+
+import net.sf.jsqlparser.JSQLParserException;
+import net.sf.jsqlparser.test.TestUtils;
+import org.junit.jupiter.api.Test;
+
+public class PostgresTest {
+    @Test
+    public void testExtractFunction() throws JSQLParserException {
+        String sqlStr = "SELECT EXTRACT(HOUR FROM TIMESTAMP '2001-02-16 20:38:40')";
+        TestUtils.assertSqlCanBeParsedAndDeparsed(sqlStr, true);
+
+        sqlStr = "SELECT EXTRACT('HOUR' FROM TIMESTAMP '2001-02-16 20:38:40')";
+        TestUtils.assertSqlCanBeParsedAndDeparsed(sqlStr, true);
+
+        sqlStr = "SELECT EXTRACT('HOURS' FROM TIMESTAMP '2001-02-16 20:38:40')";
+        TestUtils.assertSqlCanBeParsedAndDeparsed(sqlStr, true);
+    }
+
+    @Test
+    public void testExtractFunctionIssue1582() throws JSQLParserException {
+        String sqlStr = "" +
+                "select\n" +
+                "              t0.operatienr\n" +
+                "            , case\n" +
+                "                when\n" +
+                "                    case when (t0.vc_begintijd_operatie is null or lpad((extract('hours' from t0.vc_begintijd_operatie::timestamp))::text,2,'0') ||':'|| lpad(extract('minutes' from t0.vc_begintijd_operatie::timestamp)::text,2,'0') = '00:00') then null\n" +
+                "                         else (greatest(((extract('hours' from (t0.vc_eindtijd_operatie::timestamp-t0.vc_begintijd_operatie::timestamp))*60 + extract('minutes' from (t0.vc_eindtijd_operatie::timestamp-t0.vc_begintijd_operatie::timestamp)))/60)::numeric(12,2),0))*60\n" +
+                "                end = 0 then null\n" +
+                "                    else '25. Meer dan 4 uur'\n" +
+                "                end                                                                                                                                                  \n" +
+                "              as snijtijd_interval";
+        TestUtils.assertSqlCanBeParsedAndDeparsed(sqlStr, true);
+    }
+}