sql: allow creation of partial UNIQUE WITHOUT INDEX constraints

This commit allows creation of partial `UNIQUE WITHOUT INDEX`
constraints. These partial unique constraints have a predicate to
enforce uniqueness on the subset of rows in which the predicate
evaluates to true, similar to a unique partial index.

An example of a partial `UNIQUE WITHOUT INDEX` constraint:

    CREATE TABLE t (
      a INT,
      UNIQUE WITHOUT INDEX (a) WHERE a > 0
    )

**NOTE**: these constraints are not yet correctly enforcing uniqueness
on a subset of rows in the table. This requires optimizer changes that
will come in a follow-up commit. Specifically, this commit adds support
for:

  - Creating these constraints in `CREATE TABLE` and `ALTER TABLE`.
  - Storing the predicates in table descriptor constraints.
  - Validating the predicates both during creation and during descriptor
    validation.
  - Displaying the predicates in `SHOW CREATE` and `SHOW CONSTRAINTS`
    output, and in the pg_catalog.pg_constraint table.
  - Accessing the predicates via the opt catalog.

The primary motivation for this change is to simplify testing for
implicitly partitioned partial unique indexes. An experimental session
setting is required to use `UNIQUE WITHOUT INDEX` there are no current
plans to make these constraints available to users by default.

Informs cockroachdb#59195

There is no release note because these constraints are gated behind the
experimental_enable_unique_without_index_constraints session variable.

Release note: None

pkg/sql/alter_table.go

@@ -191,8 +191,10 @@ func (n *alterTableNode) startExec(params runParams) error {
 						params.SessionData(),
 						d,
 						n.tableDesc,
+						*tn,
 						NonEmptyTable,
 						t.ValidationBehavior,
+						params.p.SemaCtx(),
 					); err != nil {
 						return err
 					}

pkg/sql/catalog/descpb/structured.go

@@ -362,3 +362,8 @@ func (u *UniqueWithoutIndexConstraint) IsValidReferencedUniqueConstraint(
 func (u *UniqueWithoutIndexConstraint) GetName() string {
 	return u.Name
 }
+
+// IsPartial returns true if the constraint is a partial unique constraint.
+func (u *UniqueWithoutIndexConstraint) IsPartial() bool {
+	return u.Predicate != ""
+}

pkg/sql/catalog/descpb/structured.proto

@@ -113,6 +113,11 @@ message UniqueWithoutIndexConstraint {
                                         (gogoproto.casttype) = "ColumnID"];
   optional string name = 3 [(gogoproto.nullable) = false];
   optional ConstraintValidity validity = 4 [(gogoproto.nullable) = false];
+
+  // Predicate, if it's not empty, indicates that the constraint is a partial
+  // unique constraint with Predicate as the expression. Columns are referred to
+  // in the expression by their name.
+  optional string predicate = 5 [(gogoproto.nullable) = false];
 }
 
 message ColumnDescriptor {

pkg/sql/catalog/schemaexpr/BUILD.bazel

@@ -13,6 +13,7 @@ go_library(
         "expr_filter.go",
         "partial_index.go",
         "select_name_resolution.go",
+        "unique_contraint.go",
     ],
     importpath = "github.com/cockroachdb/cockroach/pkg/sql/catalog/schemaexpr",
     visibility = ["//visibility:public"],

pkg/sql/catalog/schemaexpr/unique_contraint.go

@@ -0,0 +1,54 @@
+// Copyright 2021 The Cockroach Authors.
+//
+// Use of this software is governed by the Business Source License
+// included in the file licenses/BSL.txt.
+//
+// As of the Change Date specified in that file, in accordance with
+// the Business Source License, use of this software will be governed
+// by the Apache License, Version 2.0, included in the file
+// licenses/APL.txt.
+
+package schemaexpr
+
+import (
+	"context"
+
+	"github.com/cockroachdb/cockroach/pkg/sql/catalog"
+	"github.com/cockroachdb/cockroach/pkg/sql/sem/tree"
+	"github.com/cockroachdb/cockroach/pkg/sql/types"
+)
+
+// ValidateUniqueWithoutIndexPredicate verifies that an expression is a valid
+// unique without index predicate. If the expression is valid, it returns the
+// serialized expression with the columns dequalified.
+//
+// A predicate expression is valid if all of the following are true:
+//
+//   - It results in a boolean.
+//   - It refers only to columns in the table.
+//   - It does not include subqueries.
+//   - It does not include non-immutable, aggregate, window, or set returning
+//     functions.
+//
+func ValidateUniqueWithoutIndexPredicate(
+	ctx context.Context,
+	tn tree.TableName,
+	desc catalog.TableDescriptor,
+	pred tree.Expr,
+	semaCtx *tree.SemaContext,
+) (string, error) {
+	expr, _, err := DequalifyAndValidateExpr(
+		ctx,
+		desc,
+		pred,
+		types.Bool,
+		"unique without index predicate",
+		semaCtx,
+		tree.VolatilityImmutable,
+		&tn,
+	)
+	if err != nil {
+		return "", err
+	}
+	return expr, nil
+}

pkg/sql/catalog/tabledesc/structured.go

@@ -2220,6 +2220,24 @@ func (desc *wrapper) validateUniqueWithoutIndexConstraints(
 			}
 			seen.Add(int(colID))
 		}
+
+		if c.IsPartial() {
+			expr, err := parser.ParseExpr(c.Predicate)
+			if err != nil {
+				return err
+			}
+			valid, err := schemaexpr.HasValidColumnReferences(desc, expr)
+			if err != nil {
+				return err
+			}
+			if !valid {
+				return fmt.Errorf(
+					"partial unique without index constraint %q refers to unknown columns in predicate: %s",
+					c.Name,
+					c.Predicate,
+				)
+			}
+		}
 	}
 
 	return nil
@@ -3458,7 +3476,7 @@ func (desc *Mutable) AddForeignKeyMutation(
 	desc.addMutation(m)
 }
 
-// AddUniqueWithoutIndexMutation adds a unqiue without index constraint mutation
+// AddUniqueWithoutIndexMutation adds a unique without index constraint mutation
 // to desc.Mutations.
 func (desc *Mutable) AddUniqueWithoutIndexMutation(
 	uc *descpb.UniqueWithoutIndexConstraint, direction descpb.DescriptorMutation_Direction,

pkg/sql/catalog/tabledesc/validate_test.go

@@ -196,6 +196,16 @@ var validationMap = []struct {
 			"Match":             {status: thisFieldReferencesNoObjects},
 		},
 	},
+	{
+		obj: descpb.UniqueWithoutIndexConstraint{},
+		fieldMap: map[string]validationStatusInfo{
+			"TableID":   {status: iSolemnlySwearThisFieldIsValidated},
+			"ColumnIDs": {status: iSolemnlySwearThisFieldIsValidated},
+			"Name":      {status: thisFieldReferencesNoObjects},
+			"Validity":  {status: thisFieldReferencesNoObjects},
+			"Predicate": {status: iSolemnlySwearThisFieldIsValidated},
+		},
+	},
 	{
 		obj: descpb.TypeDescriptor{},
 		fieldMap: map[string]validationStatusInfo{

pkg/sql/create_table.go

@@ -640,7 +640,13 @@ func addUniqueWithoutIndexColumnTableDef(
 	}
 	// Add a unique constraint.
 	if err := ResolveUniqueWithoutIndexConstraint(
-		ctx, desc, string(d.Unique.ConstraintName), []string{string(d.Name)}, ts, validationBehavior,
+		ctx,
+		desc,
+		string(d.Unique.ConstraintName),
+		[]string{string(d.Name)},
+		"", /* predicate */
+		ts,
+		validationBehavior,
 	); err != nil {
 		return err
 	}
@@ -656,8 +662,10 @@ func addUniqueWithoutIndexTableDef(
 	sessionData *sessiondata.SessionData,
 	d *tree.UniqueConstraintTableDef,
 	desc *tabledesc.Mutable,
+	tn tree.TableName,
 	ts TableState,
 	validationBehavior tree.ValidationBehavior,
+	semaCtx *tree.SemaContext,
 ) error {
 	if !evalCtx.Settings.Version.IsActive(ctx, clusterversion.UniqueWithoutIndexConstraints) {
 		return pgerror.Newf(pgcode.FeatureNotSupported,
@@ -684,20 +692,26 @@ func addUniqueWithoutIndexTableDef(
 			"partitioned unique constraints without an index are not supported",
 		)
 	}
+
+	// If there is a predicate, validate it.
+	var predicate string
 	if d.Predicate != nil {
-		// TODO(rytaft): It may be necessary to support predicates so that partial
-		// unique indexes will work correctly in multi-region deployments.
-		return pgerror.New(pgcode.FeatureNotSupported,
-			"unique constraints with a predicate but without an index are not supported",
+		var err error
+		predicate, err = schemaexpr.ValidateUniqueWithoutIndexPredicate(
+			ctx, tn, desc, d.Predicate, semaCtx,
 		)
+		if err != nil {
+			return err
+		}
 	}
+
 	// Add a unique constraint.
 	colNames := make([]string, len(d.Columns))
 	for i := range colNames {
 		colNames[i] = string(d.Columns[i].Column)
 	}
 	if err := ResolveUniqueWithoutIndexConstraint(
-		ctx, desc, string(d.Name), colNames, ts, validationBehavior,
+		ctx, desc, string(d.Name), colNames, predicate, ts, validationBehavior,
 	); err != nil {
 		return err
 	}
@@ -716,6 +730,7 @@ func ResolveUniqueWithoutIndexConstraint(
 	tbl *tabledesc.Mutable,
 	constraintName string,
 	colNames []string,
+	predicate string,
 	ts TableState,
 	validationBehavior tree.ValidationBehavior,
 ) error {
@@ -772,6 +787,7 @@ func ResolveUniqueWithoutIndexConstraint(
 		Name:      constraintName,
 		TableID:   tbl.ID,
 		ColumnIDs: columnIDs,
+		Predicate: predicate,
 		Validity:  validity,
 	}
 
@@ -2156,7 +2172,7 @@ func NewTableDesc(
 		case *tree.UniqueConstraintTableDef:
 			if d.WithoutIndex {
 				if err := addUniqueWithoutIndexTableDef(
-					ctx, evalCtx, sessionData, d, &desc, NewTable, tree.ValidationDefault,
+					ctx, evalCtx, sessionData, d, &desc, n.Table, NewTable, tree.ValidationDefault, semaCtx,
 				); err != nil {
 					return nil, err
 				}

pkg/sql/logictest/testdata/logic_test/alter_table

@@ -1471,7 +1471,17 @@ ALTER TABLE unique_without_index ADD COLUMN f INT UNIQUE WITHOUT INDEX
 # constraint.
 statement ok
 ALTER TABLE unique_without_index ADD COLUMN f INT;
-ALTER TABLE unique_without_index ADD CONSTRAINT my_unique_f UNIQUE WITHOUT INDEX (f)
+ALTER TABLE unique_without_index ADD CONSTRAINT my_unique_f UNIQUE WITHOUT INDEX (f);
+ALTER TABLE unique_without_index ADD CONSTRAINT my_partial_unique_f UNIQUE WITHOUT INDEX (f) WHERE f > 0
+
+# The unique constraint predicate must be valid. It cannot reference
+# non-existent columns.
+# TODO(mgartner): If we ever decide to make UNIQUE WITHOUT INDEX available
+# without the experimental setting, we should test that other types of invalid
+# predicates produce errors. There are similar tests in the partial_index
+# logictests that would be a good starting point.
+statement error column "g" does not exist
+ALTER TABLE unique_without_index ADD CONSTRAINT bad_partial_unique UNIQUE WITHOUT INDEX (f) WHERE g > 0
 
 # The unique constraint prevents new duplicate values.
 statement error pgcode 23505 pq: duplicate key value violates unique constraint "my_unique_f"\nDETAIL: Key \(f\)=\(1\) already exists\.
@@ -1508,17 +1518,18 @@ ALTER TABLE unique_without_index VALIDATE CONSTRAINT unique_without_index_c_key
 query TTTTB colnames
 SHOW CONSTRAINTS FROM unique_without_index
 ----
-table_name            constraint_name             constraint_type  details                             validated
-unique_without_index  my_unique_e                 UNIQUE           UNIQUE WITHOUT INDEX (e)            true
-unique_without_index  my_unique_e2                UNIQUE           UNIQUE WITHOUT INDEX (e) NOT VALID  false
-unique_without_index  my_unique_f                 UNIQUE           UNIQUE WITHOUT INDEX (f)            true
-unique_without_index  unique_a_b                  UNIQUE           UNIQUE WITHOUT INDEX (a, b)         true
-unique_without_index  unique_b                    UNIQUE           UNIQUE WITHOUT INDEX (b)            true
-unique_without_index  unique_b_1                  UNIQUE           UNIQUE WITHOUT INDEX (b)            true
-unique_without_index  unique_c                    UNIQUE           UNIQUE WITHOUT INDEX (c)            true
-unique_without_index  unique_d                    UNIQUE           UNIQUE WITHOUT INDEX (d)            true
-unique_without_index  unique_d_e                  UNIQUE           UNIQUE WITHOUT INDEX (d, e)         true
-unique_without_index  unique_without_index_c_key  UNIQUE           UNIQUE (c ASC)                      true
+table_name            constraint_name             constraint_type  details                                 validated
+unique_without_index  my_partial_unique_f         UNIQUE           UNIQUE WITHOUT INDEX (f) WHERE (f > 0)  true
+unique_without_index  my_unique_e                 UNIQUE           UNIQUE WITHOUT INDEX (e)                true
+unique_without_index  my_unique_e2                UNIQUE           UNIQUE WITHOUT INDEX (e) NOT VALID      false
+unique_without_index  my_unique_f                 UNIQUE           UNIQUE WITHOUT INDEX (f)                true
+unique_without_index  unique_a_b                  UNIQUE           UNIQUE WITHOUT INDEX (a, b)             true
+unique_without_index  unique_b                    UNIQUE           UNIQUE WITHOUT INDEX (b)                true
+unique_without_index  unique_b_1                  UNIQUE           UNIQUE WITHOUT INDEX (b)                true
+unique_without_index  unique_c                    UNIQUE           UNIQUE WITHOUT INDEX (c)                true
+unique_without_index  unique_d                    UNIQUE           UNIQUE WITHOUT INDEX (d)                true
+unique_without_index  unique_d_e                  UNIQUE           UNIQUE WITHOUT INDEX (d, e)             true
+unique_without_index  unique_without_index_c_key  UNIQUE           UNIQUE (c ASC)                          true
 
 statement ok
 ALTER TABLE unique_without_index RENAME COLUMN a TO aa
@@ -1535,16 +1546,17 @@ ALTER TABLE unique_without_index RENAME CONSTRAINT unique_b TO unique_b_2
 query TTTTB
 SHOW CONSTRAINTS FROM unique_without_index
 ----
-unique_without_index  my_unique_e                 UNIQUE  UNIQUE WITHOUT INDEX (e)            true
-unique_without_index  my_unique_e2                UNIQUE  UNIQUE WITHOUT INDEX (e) NOT VALID  false
-unique_without_index  my_unique_f                 UNIQUE  UNIQUE WITHOUT INDEX (f)            true
-unique_without_index  unique_a_b                  UNIQUE  UNIQUE WITHOUT INDEX (aa, b)        true
-unique_without_index  unique_b_1                  UNIQUE  UNIQUE WITHOUT INDEX (b)            true
-unique_without_index  unique_b_2                  UNIQUE  UNIQUE WITHOUT INDEX (b)            true
-unique_without_index  unique_c                    UNIQUE  UNIQUE WITHOUT INDEX (c)            true
-unique_without_index  unique_d                    UNIQUE  UNIQUE WITHOUT INDEX (d)            true
-unique_without_index  unique_d_e                  UNIQUE  UNIQUE WITHOUT INDEX (d, e)         true
-unique_without_index  unique_without_index_c_key  UNIQUE  UNIQUE (c ASC)                      true
+unique_without_index  my_partial_unique_f         UNIQUE  UNIQUE WITHOUT INDEX (f) WHERE (f > 0)  true
+unique_without_index  my_unique_e                 UNIQUE  UNIQUE WITHOUT INDEX (e)                true
+unique_without_index  my_unique_e2                UNIQUE  UNIQUE WITHOUT INDEX (e) NOT VALID      false
+unique_without_index  my_unique_f                 UNIQUE  UNIQUE WITHOUT INDEX (f)                true
+unique_without_index  unique_a_b                  UNIQUE  UNIQUE WITHOUT INDEX (aa, b)            true
+unique_without_index  unique_b_1                  UNIQUE  UNIQUE WITHOUT INDEX (b)                true
+unique_without_index  unique_b_2                  UNIQUE  UNIQUE WITHOUT INDEX (b)                true
+unique_without_index  unique_c                    UNIQUE  UNIQUE WITHOUT INDEX (c)                true
+unique_without_index  unique_d                    UNIQUE  UNIQUE WITHOUT INDEX (d)                true
+unique_without_index  unique_d_e                  UNIQUE  UNIQUE WITHOUT INDEX (d, e)             true
+unique_without_index  unique_without_index_c_key  UNIQUE  UNIQUE (c ASC)                          true
 
 statement error pgcode 0A000 cannot drop UNIQUE constraint \"unique_without_index_c_key\"
 ALTER TABLE unique_without_index DROP CONSTRAINT unique_without_index_c_key
@@ -1563,14 +1575,15 @@ ALTER TABLE unique_without_index DROP CONSTRAINT my_unique_e2
 query TTTTB
 SHOW CONSTRAINTS FROM unique_without_index
 ----
-unique_without_index  my_unique_e                 UNIQUE  UNIQUE WITHOUT INDEX (e)      true
-unique_without_index  my_unique_f                 UNIQUE  UNIQUE WITHOUT INDEX (f)      true
-unique_without_index  unique_a_b                  UNIQUE  UNIQUE WITHOUT INDEX (aa, b)  true
-unique_without_index  unique_b_1                  UNIQUE  UNIQUE WITHOUT INDEX (b)      true
-unique_without_index  unique_c                    UNIQUE  UNIQUE WITHOUT INDEX (c)      true
-unique_without_index  unique_d                    UNIQUE  UNIQUE WITHOUT INDEX (d)      true
-unique_without_index  unique_d_e                  UNIQUE  UNIQUE WITHOUT INDEX (d, e)   true
-unique_without_index  unique_without_index_c_key  UNIQUE  UNIQUE (c ASC)                true
+unique_without_index  my_partial_unique_f         UNIQUE  UNIQUE WITHOUT INDEX (f) WHERE (f > 0)  true
+unique_without_index  my_unique_e                 UNIQUE  UNIQUE WITHOUT INDEX (e)                true
+unique_without_index  my_unique_f                 UNIQUE  UNIQUE WITHOUT INDEX (f)                true
+unique_without_index  unique_a_b                  UNIQUE  UNIQUE WITHOUT INDEX (aa, b)            true
+unique_without_index  unique_b_1                  UNIQUE  UNIQUE WITHOUT INDEX (b)                true
+unique_without_index  unique_c                    UNIQUE  UNIQUE WITHOUT INDEX (c)                true
+unique_without_index  unique_d                    UNIQUE  UNIQUE WITHOUT INDEX (d)                true
+unique_without_index  unique_d_e                  UNIQUE  UNIQUE WITHOUT INDEX (d, e)             true
+unique_without_index  unique_without_index_c_key  UNIQUE  UNIQUE (c ASC)                          true
 
 # Dropping a column in a unique constraint drops the constraint.
 statement ok
@@ -1579,12 +1592,13 @@ ALTER TABLE unique_without_index DROP COLUMN b
 query TTTTB
 SHOW CONSTRAINTS FROM unique_without_index
 ----
-unique_without_index  my_unique_e                 UNIQUE  UNIQUE WITHOUT INDEX (e)     true
-unique_without_index  my_unique_f                 UNIQUE  UNIQUE WITHOUT INDEX (f)     true
-unique_without_index  unique_c                    UNIQUE  UNIQUE WITHOUT INDEX (c)     true
-unique_without_index  unique_d                    UNIQUE  UNIQUE WITHOUT INDEX (d)     true
-unique_without_index  unique_d_e                  UNIQUE  UNIQUE WITHOUT INDEX (d, e)  true
-unique_without_index  unique_without_index_c_key  UNIQUE  UNIQUE (c ASC)               true
+unique_without_index  my_partial_unique_f         UNIQUE  UNIQUE WITHOUT INDEX (f) WHERE (f > 0)  true
+unique_without_index  my_unique_e                 UNIQUE  UNIQUE WITHOUT INDEX (e)                true
+unique_without_index  my_unique_f                 UNIQUE  UNIQUE WITHOUT INDEX (f)                true
+unique_without_index  unique_c                    UNIQUE  UNIQUE WITHOUT INDEX (c)                true
+unique_without_index  unique_d                    UNIQUE  UNIQUE WITHOUT INDEX (d)                true
+unique_without_index  unique_d_e                  UNIQUE  UNIQUE WITHOUT INDEX (d, e)             true
+unique_without_index  unique_without_index_c_key  UNIQUE  UNIQUE (c ASC)                          true
 
 query TTTTB
 SHOW CONSTRAINTS FROM uwi_child
@@ -1603,10 +1617,11 @@ ALTER TABLE unique_without_index DROP COLUMN d CASCADE
 query TTTTB
 SHOW CONSTRAINTS FROM unique_without_index
 ----
-unique_without_index  my_unique_e                 UNIQUE  UNIQUE WITHOUT INDEX (e)  true
-unique_without_index  my_unique_f                 UNIQUE  UNIQUE WITHOUT INDEX (f)  true
-unique_without_index  unique_c                    UNIQUE  UNIQUE WITHOUT INDEX (c)  true
-unique_without_index  unique_without_index_c_key  UNIQUE  UNIQUE (c ASC)            true
+unique_without_index  my_partial_unique_f         UNIQUE  UNIQUE WITHOUT INDEX (f) WHERE (f > 0)  true
+unique_without_index  my_unique_e                 UNIQUE  UNIQUE WITHOUT INDEX (e)                true
+unique_without_index  my_unique_f                 UNIQUE  UNIQUE WITHOUT INDEX (f)                true
+unique_without_index  unique_c                    UNIQUE  UNIQUE WITHOUT INDEX (c)                true
+unique_without_index  unique_without_index_c_key  UNIQUE  UNIQUE (c ASC)                          true
 
 query TTTTB
 SHOW CONSTRAINTS FROM uwi_child

pkg/sql/logictest/testdata/logic_test/create_table

@@ -403,8 +403,17 @@ CREATE TABLE error (a INT, b INT, UNIQUE WITHOUT INDEX (a) PARTITION BY LIST (b)
   PARTITION p1 VALUES IN (1)
 ))
 
-statement error pgcode 0A000 unique constraints with a predicate but without an index are not supported
-CREATE TABLE error (a INT, b INT, UNIQUE WITHOUT INDEX (a) WHERE b > 5)
+# The unique constraint predicate must be valid. It cannot reference
+# non-existent columns.
+# TODO(mgartner): If we ever decide to make UNIQUE WITHOUT INDEX available
+# without the experimental setting, we should test that other types of invalid
+# predicates produce errors. There are similar tests in the partial_index
+# logictests that would be a good starting point.
+statement error column "c" does not exist
+CREATE TABLE unique_without_index_partial (a INT, b INT, UNIQUE WITHOUT INDEX (a) WHERE c > 0)
+
+statement ok
+CREATE TABLE unique_without_index_partial (a INT, b INT, UNIQUE WITHOUT INDEX (a) WHERE b > 5)
 
 subtest regression_57630