Return precision values for non-decimal columns

This PR makes `ResultSetMetaData#getPrecision()` to return non-zero
values for integral numbers, floating point, date/time and string
columns.

Unlike the `DECIMAL` type, where actual column precision is returned,
for other types this call is expected to give a hint to a client
software how much space the textual representation of the field is
going to take. Previously returned 0 value appeared to cause problems
in some of such clients.

Values returned are consistent with ones returned by Postgres.

Testing: new test added for all types.

Fixes: duckdb#340

Author: staticlibs

src/main/java/org/duckdb/DuckDBResultSetMetaData.java

@@ -310,17 +310,58 @@ public int getColumnDisplaySize(int column) throws SQLException {
     }
 
     public int getPrecision(int column) throws SQLException {
-        DuckDBColumnTypeMetaData typeMetaData = typeMetadataForColumn(column);
+        checkColumn(column);
+        DuckDBColumnTypeMetaData typeMetaData = column_types_meta[column - 1];
 
-        if (typeMetaData == null) {
-            return 0;
+        if (typeMetaData != null) {
+            return typeMetaData.width;
         }
 
-        return typeMetaData.width;
+        DuckDBColumnType colType = column_types[column - 1];
+        switch (colType) {
+        case BOOLEAN:
+            return 5;
+        case TINYINT:
+        case UTINYINT:
+            return 3;
+        case SMALLINT:
+        case USMALLINT:
+            return 5;
+        case INTEGER:
+        case UINTEGER:
+            return 10;
+        case BIGINT:
+        case UBIGINT:
+            return 19;
+        case HUGEINT:
+        case UHUGEINT:
+            return 38;
+        case FLOAT:
+            return 8;
+        case DOUBLE:
+            return 17;
+        case TIME:
+            return 15;
+        case DATE:
+            return 13;
+        case TIMESTAMP:
+        case TIMESTAMP_MS:
+        case TIMESTAMP_NS:
+        case TIMESTAMP_S:
+            return 29;
+        case TIMESTAMP_WITH_TIME_ZONE:
+            return 35;
+        case VARCHAR:
+        case BLOB:
+            return Integer.MAX_VALUE;
+        default:
+            return 0;
+        }
     }
 
     public int getScale(int column) throws SQLException {
-        DuckDBColumnTypeMetaData typeMetaData = typeMetadataForColumn(column);
+        checkColumn(column);
+        DuckDBColumnTypeMetaData typeMetaData = column_types_meta[column - 1];
 
         if (typeMetaData == null) {
             return 0;
@@ -347,10 +388,9 @@ public boolean isWrapperFor(Class<?> iface) {
         return iface.isInstance(this);
     }
 
-    private DuckDBColumnTypeMetaData typeMetadataForColumn(int columnIndex) throws SQLException {
+    private void checkColumn(int columnIndex) throws SQLException {
         if (columnIndex > column_count) {
             throw new SQLException("Column index out of bounds");
         }
-        return column_types_meta[columnIndex - 1];
     }
 }

src/test/java/org/duckdb/TestResults.java

@@ -8,6 +8,7 @@
 import java.math.BigInteger;
 import java.sql.*;
 import java.time.LocalDateTime;
+import java.time.LocalTime;
 import java.util.Properties;
 import java.util.UUID;
 
@@ -297,4 +298,69 @@ public static void test_results_strings_cast() throws Exception {
             }
         }
     }
+
+    public static void test_results_precision() throws Exception {
+        try (Connection conn = DriverManager.getConnection(JDBC_URL); Statement stmt = conn.createStatement()) {
+            try (ResultSet rs = stmt.executeQuery("SELECT TRUE::BOOLEAN")) {
+                assertEquals(rs.getMetaData().getPrecision(1), 5);
+            }
+            try (ResultSet rs = stmt.executeQuery("SELECT 42::TINYINT")) {
+                assertEquals(rs.getMetaData().getPrecision(1), 3);
+            }
+            try (ResultSet rs = stmt.executeQuery("SELECT 42::UTINYINT")) {
+                assertEquals(rs.getMetaData().getPrecision(1), 3);
+            }
+            try (ResultSet rs = stmt.executeQuery("SELECT 42::SMALLINT")) {
+                assertEquals(rs.getMetaData().getPrecision(1), 5);
+            }
+            try (ResultSet rs = stmt.executeQuery("SELECT 42::USMALLINT")) {
+                assertEquals(rs.getMetaData().getPrecision(1), 5);
+            }
+            try (ResultSet rs = stmt.executeQuery("SELECT 42::INTEGER")) {
+                assertEquals(rs.getMetaData().getPrecision(1), 10);
+            }
+            try (ResultSet rs = stmt.executeQuery("SELECT 42::UINTEGER")) {
+                assertEquals(rs.getMetaData().getPrecision(1), 10);
+            }
+            try (ResultSet rs = stmt.executeQuery("SELECT 42::BIGINT")) {
+                assertEquals(rs.getMetaData().getPrecision(1), 19);
+            }
+            try (ResultSet rs = stmt.executeQuery("SELECT 42::UBIGINT")) {
+                assertEquals(rs.getMetaData().getPrecision(1), 19);
+            }
+            try (ResultSet rs = stmt.executeQuery("SELECT 42::HUGEINT")) {
+                assertEquals(rs.getMetaData().getPrecision(1), 38);
+            }
+            try (ResultSet rs = stmt.executeQuery("SELECT 42::UHUGEINT")) {
+                assertEquals(rs.getMetaData().getPrecision(1), 38);
+            }
+            try (ResultSet rs = stmt.executeQuery("SELECT 42::FLOAT")) {
+                assertEquals(rs.getMetaData().getPrecision(1), 8);
+            }
+            try (ResultSet rs = stmt.executeQuery("SELECT 42::DOUBLE")) {
+                assertEquals(rs.getMetaData().getPrecision(1), 17);
+            }
+            try (ResultSet rs = stmt.executeQuery("SELECT 42::DECIMAL(15,3)")) {
+                assertEquals(rs.getMetaData().getPrecision(1), 15);
+            }
+            try (ResultSet rs = stmt.executeQuery("SELECT NULL::TIME")) {
+                assertEquals(rs.getMetaData().getPrecision(1), 15);
+            }
+            try (ResultSet rs = stmt.executeQuery("SELECT NULL::DATE")) {
+                assertEquals(rs.getMetaData().getPrecision(1), 13);
+            }
+            try (ResultSet rs = stmt.executeQuery("SELECT NULL::TIMESTAMP")) {
+                assertEquals(rs.getMetaData().getPrecision(1), 29);
+            }
+            try (ResultSet rs = stmt.executeQuery("SELECT NULL::TIMESTAMP WITH TIME ZONE")) {
+                assertEquals(rs.getMetaData().getPrecision(1), 35);
+            }
+            try (ResultSet rs = stmt.executeQuery("SELECT NULL::VARCHAR")) {
+                assertEquals(rs.getMetaData().getPrecision(1), Integer.MAX_VALUE);
+            }
+            try (ResultSet rs = stmt.executeQuery("SELECT NULL::BLOB")) {
+                assertEquals(rs.getMetaData().getPrecision(1), Integer.MAX_VALUE);
+            }
+        }
+    }
 }