Fix inferring type of decimals with leading zeros in MongoDB

Heltman · Sep 20, 2023 · 917be6e · 917be6e
1 parent 005e84b
commit 917be6e
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Showing 2 changed files with 6 additions and 1 deletion.
diff --git a/plugin/trino-mongodb/src/main/java/io/trino/plugin/mongodb/MongoSession.java b/plugin/trino-mongodb/src/main/java/io/trino/plugin/mongodb/MongoSession.java
@@ -922,7 +922,10 @@ else if (value instanceof Decimal128 decimal128) {
             catch (ArithmeticException e) {
                 return Optional.empty();
             }
-            typeSignature = createDecimalType(decimal.precision(), decimal.scale()).getTypeSignature();
+            // Java's BigDecimal.precision() returns precision for the unscaled value, so it skips leading zeros for values lower than 1.
+            // Trino's (SQL) decimal precision must include leading zeros in values less than 1, and can never be lower than scale.
+            int precision = Math.max(decimal.precision(), decimal.scale());
+            typeSignature = createDecimalType(precision, decimal.scale()).getTypeSignature();
         }
         else if (value instanceof Date) {
             typeSignature = TIMESTAMP_MILLIS.getTypeSignature();

diff --git a/plugin/trino-mongodb/src/test/java/io/trino/plugin/mongodb/TestMongoTypeMapping.java b/plugin/trino-mongodb/src/test/java/io/trino/plugin/mongodb/TestMongoTypeMapping.java
@@ -190,6 +190,8 @@ public void testDecimal()
                 .addRoundTrip("NumberDecimal(\"2\")", "CAST('2' AS decimal(1, 0))")
                 .addRoundTrip("NumberDecimal(\"2.3\")", "CAST('2.3' AS decimal(2, 1))")
                 .addRoundTrip("NumberDecimal(\"-2.3\")", "CAST('-2.3' AS decimal(2, 1))")
+                .addRoundTrip("NumberDecimal(\"0.03\")", "CAST('0.03' AS decimal(2, 2))")
+                .addRoundTrip("NumberDecimal(\"-0.03\")", "CAST('-0.03' AS decimal(2, 2))")
                 .addRoundTrip("NumberDecimal(\"1234567890123456789012345678901234\")", "CAST('1234567890123456789012345678901234' AS decimal(34, 0))") // 34 is the max precision in Decimal128
                 .addRoundTrip("NumberDecimal(\"1234567890123456.789012345678901234\")", "CAST('1234567890123456.789012345678901234' AS decimal(34, 18))")
                 .execute(getQueryRunner(), mongoCreateAndInsert(getSession(), "tpch", "test_decimal"));