source-sqlserver: Support DATETIME as backfill keys

By default we serialize these as an RFC3339 timestamp, but SQL
Server doesn't support that as an input format for a DATETIME
column since DATETIMEs only have three digits of sub-second
precision and no time zone.

To make this work we just have to adjust the FDB row key encode
operation so that when the column type is `datetime` we apply a
different string format. This doesn't change the handling of the
actual capture output values, only row key serialization.

source-sqlserver/.snapshots/TestScanKeyTypes-DateTime

@@ -0,0 +1,49 @@
+####################################
+### Capture from Start
+####################################
+# ================================
+# Collection "acmeCo/test/test_scankeytypes_datetime_889298060005": 1 Documents
+# ================================
+{"_meta":{"op":"c","source":{"schema":"dbo","snapshot":true,"table":"test_ScanKeyTypes_DateTime_889298060005","lsn":"","seqval":"AAAAAAAAAAAAAA=="}},"k":"<TIMESTAMP>","v":"Data 0"}
+# ================================
+# Final State Checkpoint
+# ================================
+{"bindingStateV1":{"dbo%2Ftest_ScanKeyTypes_DateTime_889298060005":{"backfilled":1,"key_columns":["k"],"mode":"Backfill","scanned":"AjE5OTEtMDgtMzFUMTI6MzQ6NTQuMTEwAA=="}},"cursor":"AAAAAAAAAAAAAA=="}
+
+
+####################################
+### Capture from Key "AjE5OTEtMDgtMzFUMTI6MzQ6NTQuMTEwAA=="
+####################################
+# ================================
+# Collection "acmeCo/test/test_scankeytypes_datetime_889298060005": 1 Documents
+# ================================
+{"_meta":{"op":"c","source":{"schema":"dbo","snapshot":true,"table":"test_ScanKeyTypes_DateTime_889298060005","lsn":"","seqval":"AAAAAAAAAAAAAA=="}},"k":"<TIMESTAMP>","v":"Data 1"}
+# ================================
+# Final State Checkpoint
+# ================================
+{"bindingStateV1":{"dbo%2Ftest_ScanKeyTypes_DateTime_889298060005":{"backfilled":2,"key_columns":["k"],"mode":"Backfill","scanned":"AjE5OTEtMDgtMzFUMTI6MzQ6NTQuMzMzAA=="}},"cursor":"AAAAAAAAAAAAAA=="}
+
+
+####################################
+### Capture from Key "AjE5OTEtMDgtMzFUMTI6MzQ6NTQuMzMzAA=="
+####################################
+# ================================
+# Collection "acmeCo/test/test_scankeytypes_datetime_889298060005": 1 Documents
+# ================================
+{"_meta":{"op":"c","source":{"schema":"dbo","snapshot":true,"table":"test_ScanKeyTypes_DateTime_889298060005","lsn":"","seqval":"AAAAAAAAAAAAAA=="}},"k":"<TIMESTAMP>","v":"Data 2"}
+# ================================
+# Final State Checkpoint
+# ================================
+{"bindingStateV1":{"dbo%2Ftest_ScanKeyTypes_DateTime_889298060005":{"backfilled":3,"key_columns":["k"],"mode":"Backfill","scanned":"AjIwMDAtMDEtMDFUMDE6MDE6MDEuMDAwAA=="}},"cursor":"AAAAAAAAAAAAAA=="}
+
+
+####################################
+### Capture from Key "AjIwMDAtMDEtMDFUMDE6MDE6MDEuMDAwAA=="
+####################################
+# ================================
+# Final State Checkpoint
+# ================================
+{"bindingStateV1":{"dbo%2Ftest_ScanKeyTypes_DateTime_889298060005":{"backfilled":3,"key_columns":["k"],"mode":"Active"}},"cursor":"AAAAAAAAAAAAAA=="}
+
+
+

source-sqlserver/datatypes.go

@@ -15,6 +15,12 @@ const (
 	// thus it can be sorted lexicographically as bytes.
 	sortableRFC3339Nano = "2006-01-02T15:04:05.000000000Z07:00"
 
+	// In order to be round-tripped successfully as a backfill key, datetimes must be
+	// serialized to a string with three decimal digits of precision and no time zone.
+	// This is only done for row key serialization, not the actual values in a capture's
+	// output documents.
+	datetimeKeyEncoding = "2006-01-02T15:04:05.000"
+
 	// SQL Server sort ordering for `uniqueidentifier` columns is absolutely insane,
 	// so we have to reshuffle the underlying bytes pretty hard to produce a row key
 	// whose bytewise lexicographic ordering matches SQL Server sorting rules.
@@ -35,7 +41,12 @@ const (
 func encodeKeyFDB(key, ktype interface{}) (tuple.TupleElement, error) {
 	switch key := key.(type) {
 	case time.Time:
-		return key.Format(sortableRFC3339Nano), nil
+		switch ktype {
+		case "datetime":
+			return key.Format(datetimeKeyEncoding), nil
+		default:
+			return key.Format(sortableRFC3339Nano), nil
+		}
 	case []byte:
 		switch ktype {
 		case "uniqueidentifier":

source-sqlserver/datatypes_test.go

@@ -89,6 +89,7 @@ func TestScanKeyTypes(t *testing.T) {
 		}},
 		{"Numeric", "NUMERIC(10,5)", []any{"-1234", "0", "-3", "2", "12345.12", "12345.121", "12345.1205", "12345.12059", "12346"}},
 		{"Decimal", "DECIMAL(10,5)", []any{"-1234", "0", "-3", "2", "12345.12", "12345.121", "12345.1205", "12345.12059", "12346"}},
+		{"DateTime", "DATETIME", []any{"1991-08-31T12:34:54.111", "1991-08-31T12:34:54.333", "2000-01-01T01:01:01"}},
 	} {
 		t.Run(tc.Name, func(t *testing.T) {
 			var uniqueID = fmt.Sprintf("88929806%04d", idx)