[FLINK-36970][cdc-common] Merge result of data type BIGINT and DOUBLE should be DOUBLE instead of STRING

This closes #3821

flink-cdc-common/src/main/java/org/apache/flink/cdc/common/utils/SchemaMergingUtils.java

@@ -810,7 +810,9 @@ public class SchemaMergingUtils {
         mergingTree.put(DoubleType.class, ImmutableList.of(doubleType, stringType));
         mergingTree.put(FloatType.class, ImmutableList.of(floatType, doubleType, stringType));
         mergingTree.put(DecimalType.class, ImmutableList.of(stringType));
-        mergingTree.put(BigIntType.class, ImmutableList.of(bigIntType, decimalType, stringType));
+        mergingTree.put(
+                BigIntType.class,
+                ImmutableList.of(bigIntType, decimalType, doubleType, stringType));
         mergingTree.put(
                 IntType.class,
                 ImmutableList.of(intType, bigIntType, decimalType, doubleType, stringType));

flink-cdc-common/src/test/java/org/apache/flink/cdc/common/utils/SchemaMergingUtilsTest.java

@@ -975,7 +975,7 @@ class SchemaMergingUtilsTest {
                         DECIMAL, FLOAT, DOUBLE, STRING, STRING, STRING, STRING, STRING, STRING,
                         STRING));
 
-        // 16-bit TINYINT could fit into FLOAT (24 sig bits) or DOUBLE (53 sig bits)
+        // 16-bit SMALLINT could fit into FLOAT (24 sig bits) or DOUBLE (53 sig bits)
         assertTypeMergingVector(
                 SMALLINT,
                 Arrays.asList(
@@ -983,7 +983,7 @@ class SchemaMergingUtilsTest {
                         DECIMAL, FLOAT, DOUBLE, STRING, STRING, STRING, STRING, STRING, STRING,
                         STRING));
 
-        // 32-bit TINYINT could fit into DOUBLE (53 sig bits)
+        // 32-bit INT could fit into DOUBLE (53 sig bits)
         assertTypeMergingVector(
                 INT,
                 Arrays.asList(
@@ -994,7 +994,7 @@ class SchemaMergingUtilsTest {
                 BIGINT,
                 Arrays.asList(
                         STRING, STRING, STRING, STRING, STRING, BIGINT, BIGINT, BIGINT, BIGINT,
-                        DECIMAL, STRING, STRING, STRING, STRING, STRING, STRING, STRING, STRING,
+                        DECIMAL, DOUBLE, DOUBLE, STRING, STRING, STRING, STRING, STRING, STRING,
                         STRING));
 
         assertTypeMergingVector(
@@ -1007,14 +1007,14 @@ class SchemaMergingUtilsTest {
         assertTypeMergingVector(
                 FLOAT,
                 Arrays.asList(
-                        STRING, STRING, STRING, STRING, STRING, FLOAT, FLOAT, DOUBLE, STRING,
+                        STRING, STRING, STRING, STRING, STRING, FLOAT, FLOAT, DOUBLE, DOUBLE,
                         STRING, FLOAT, DOUBLE, STRING, STRING, STRING, STRING, STRING, STRING,
                         STRING));
 
         assertTypeMergingVector(
                 DOUBLE,
                 Arrays.asList(
-                        STRING, STRING, STRING, STRING, STRING, DOUBLE, DOUBLE, DOUBLE, STRING,
+                        STRING, STRING, STRING, STRING, STRING, DOUBLE, DOUBLE, DOUBLE, DOUBLE,
                         STRING, DOUBLE, DOUBLE, STRING, STRING, STRING, STRING, STRING, STRING,
                         STRING));