function_traits.go

// Copyright 2017 PingCAP, Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package expression

import (
	"github.com/pingcap/tidb/pkg/parser/ast"
	"github.com/pingcap/tidb/pkg/parser/opcode"
)

// UnCacheableFunctions stores functions which can not be cached to plan cache.
var UnCacheableFunctions = map[string]struct{}{
	ast.Database:             {},
	ast.CurrentUser:          {},
	ast.CurrentRole:          {},
	ast.CurrentResourceGroup: {},
	ast.User:                 {},
	ast.ConnectionID:         {},
	ast.LastInsertId:         {},
	ast.RowCount:             {},
	ast.Version:              {},
	ast.Like:                 {},

	// functions below are incompatible with (non-prep) plan cache, we'll fix them one by one later.
	ast.JSONExtract:      {}, // cannot pass TestFuncJSON
	ast.JSONObject:       {},
	ast.JSONArray:        {},
	ast.Coalesce:         {},
	ast.Convert:          {},
	ast.TimeLiteral:      {},
	ast.DateLiteral:      {},
	ast.TimestampLiteral: {},
	ast.AesEncrypt:       {}, // affected by @@block_encryption_mode
	ast.AesDecrypt:       {},
}

// unFoldableFunctions stores functions which can not be folded duration constant folding stage.
var unFoldableFunctions = map[string]struct{}{
	ast.Sysdate:   {},
	ast.FoundRows: {},
	ast.Rand:      {},
	ast.UUID:      {},
	ast.Sleep:     {},
	ast.RowFunc:   {},
	ast.Values:    {},
	ast.SetVar:    {},
	ast.GetVar:    {},
	ast.GetParam:  {},
	ast.Benchmark: {},
	ast.DayName:   {},
	ast.NextVal:   {},
	ast.LastVal:   {},
	ast.SetVal:    {},
	ast.AnyValue:  {},
}

// DisableFoldFunctions stores functions which prevent child scope functions from being constant folded.
// Typically, these functions shall also exist in unFoldableFunctions, to stop from being folded when they themselves
// are in child scope of an outer function, and the outer function is recursively folding its children.
var DisableFoldFunctions = map[string]struct{}{
	ast.Benchmark: {},
}

// TryFoldFunctions stores functions which try to fold constant in child scope functions if without errors/warnings,
// otherwise, the child functions do not fold constant.
// Note: the function itself should fold constant.
var TryFoldFunctions = map[string]struct{}{
	ast.If:       {},
	ast.Ifnull:   {},
	ast.Case:     {},
	ast.LogicAnd: {},
	ast.LogicOr:  {},
	ast.Coalesce: {},
	ast.Interval: {},
}

// IllegalFunctions4GeneratedColumns stores functions that is illegal for generated columns.
// See https://github.com/mysql/mysql-server/blob/5.7/mysql-test/suite/gcol/inc/gcol_blocked_sql_funcs_main.inc for details
var IllegalFunctions4GeneratedColumns = map[string]struct{}{
	ast.ConnectionID:     {},
	ast.LoadFile:         {},
	ast.LastInsertId:     {},
	ast.Rand:             {},
	ast.UUID:             {},
	ast.UUIDShort:        {},
	ast.Curdate:          {},
	ast.CurrentDate:      {},
	ast.Curtime:          {},
	ast.CurrentTime:      {},
	ast.CurrentTimestamp: {},
	ast.LocalTime:        {},
	ast.LocalTimestamp:   {},
	ast.Now:              {},
	ast.UnixTimestamp:    {},
	ast.UTCDate:          {},
	ast.UTCTime:          {},
	ast.UTCTimestamp:     {},
	ast.Benchmark:        {},
	ast.CurrentUser:      {},
	ast.Database:         {},
	ast.FoundRows:        {},
	ast.GetLock:          {},
	ast.IsFreeLock:       {},
	ast.IsUsedLock:       {},
	ast.MasterPosWait:    {},
	ast.NameConst:        {},
	ast.ReleaseLock:      {},
	ast.RowFunc:          {},
	ast.RowCount:         {},
	ast.Schema:           {},
	ast.SessionUser:      {},
	ast.Sleep:            {},
	ast.Sysdate:          {},
	ast.SystemUser:       {},
	ast.User:             {},
	ast.Values:           {},
	ast.Encrypt:          {},
	ast.Version:          {},
	ast.JSONMerge:        {},
	ast.SetVar:           {},
	ast.GetVar:           {},
	ast.ReleaseAllLocks:  {},
}

// IsDeferredFunctions checks whether the function is in DeferredFunctions.
// DeferredFunctions stores functions which are foldable but should be deferred as well when plan cache is enabled.
// Note that, these functions must be foldable at first place, i.e, they are not in `unFoldableFunctions`.
func IsDeferredFunctions(ctx BuildContext, fn string) bool {
	_, ok := deferredFunctions[fn]
	if ok {
		return ok
	}
	if fn == ast.Sysdate && ctx.GetSysdateIsNow() {
		return true
	}
	return ok
}

var deferredFunctions = map[string]struct{}{
	ast.Now:              {},
	ast.RandomBytes:      {},
	ast.CurrentTimestamp: {},
	ast.UTCTime:          {},
	ast.Curtime:          {},
	ast.CurrentTime:      {},
	ast.UTCTimestamp:     {},
	ast.UnixTimestamp:    {},
	ast.Curdate:          {},
	ast.CurrentDate:      {},
	ast.UTCDate:          {},
}

// AllowedPartitionFuncMap stores functions which can be used in the partition expression.
var AllowedPartitionFuncMap = map[string]struct{}{
	ast.ToDays:        {},
	ast.ToSeconds:     {},
	ast.DayOfMonth:    {},
	ast.Month:         {},
	ast.DayOfYear:     {},
	ast.Quarter:       {},
	ast.YearWeek:      {},
	ast.Year:          {},
	ast.Weekday:       {},
	ast.DayOfWeek:     {},
	ast.Day:           {},
	ast.Hour:          {},
	ast.Minute:        {},
	ast.Second:        {},
	ast.TimeToSec:     {},
	ast.MicroSecond:   {},
	ast.UnixTimestamp: {},
	ast.FromDays:      {},
	ast.Extract:       {},
	ast.Abs:           {},
	ast.Ceiling:       {},
	ast.DateDiff:      {},
	ast.Floor:         {},
	ast.Mod:           {},
}

// AllowedPartition4BinaryOpMap store the operator for Binary Expr
// See https://dev.mysql.com/doc/refman/5.7/en/partitioning-limitations.html for more details
var AllowedPartition4BinaryOpMap = map[opcode.Op]struct{}{
	opcode.Plus:   {},
	opcode.Minus:  {},
	opcode.Mul:    {},
	opcode.IntDiv: {},
	opcode.Mod:    {},
}

// AllowedPartition4UnaryOpMap store the operator for Unary Expr
var AllowedPartition4UnaryOpMap = map[opcode.Op]struct{}{
	opcode.Plus:  {},
	opcode.Minus: {},
}

// inequalFunctions stores functions which cannot be propagated from column equal condition.
var inequalFunctions = map[string]struct{}{
	ast.IsNull: {},
}

// mutableEffectsFunctions stores functions which are mutable or have side effects, specifically,
// we cannot remove them from filter even if they have duplicates.
var mutableEffectsFunctions = map[string]struct{}{
	// Time related functions in MySQL have various behaviors when executed multiple times in a single SQL,
	// for example:
	// mysql> select current_timestamp(), sleep(5), current_timestamp();
	// +---------------------+----------+---------------------+
	// | current_timestamp() | sleep(5) | current_timestamp() |
	// +---------------------+----------+---------------------+
	// | 2018-12-18 17:55:39 |        0 | 2018-12-18 17:55:39 |
	// +---------------------+----------+---------------------+
	// while:
	// mysql> select sysdate(), sleep(5), sysdate();
	// +---------------------+----------+---------------------+
	// | sysdate()           | sleep(5) | sysdate()           |
	// +---------------------+----------+---------------------+
	// | 2018-12-18 17:57:38 |        0 | 2018-12-18 17:57:43 |
	// +---------------------+----------+---------------------+
	// for safety consideration, treat them all as mutable.
	ast.Now:              {},
	ast.CurrentTimestamp: {},
	ast.UTCTime:          {},
	ast.Curtime:          {},
	ast.CurrentTime:      {},
	ast.UTCTimestamp:     {},
	ast.UnixTimestamp:    {},
	ast.Sysdate:          {},
	ast.Curdate:          {},
	ast.CurrentDate:      {},
	ast.UTCDate:          {},

	ast.Rand:        {},
	ast.RandomBytes: {},
	ast.UUID:        {},
	ast.UUIDShort:   {},
	ast.Sleep:       {},
	ast.SetVar:      {},
	ast.GetVar:      {},
	ast.AnyValue:    {},
}

// some functions do NOT have right implementations, but may have noop ones(like with any inputs, always return 1)
// if apps really need these "funcs" to run, we offer sys var(tidb_enable_noop_functions) to enable noop usage
var noopFuncs = map[string]struct{}{}

// booleanFunctions stores boolean functions
var booleanFunctions = map[string]struct{}{
	ast.UnaryNot:           {},
	ast.EQ:                 {},
	ast.NE:                 {},
	ast.NullEQ:             {},
	ast.LT:                 {},
	ast.LE:                 {},
	ast.GT:                 {},
	ast.GE:                 {},
	ast.In:                 {},
	ast.LogicAnd:           {},
	ast.LogicOr:            {},
	ast.LogicXor:           {},
	ast.IsTruthWithNull:    {},
	ast.IsTruthWithoutNull: {},
	ast.IsFalsity:          {},
	ast.IsNull:             {},
	ast.Like:               {},
	ast.Regexp:             {},
	ast.IsIPv4:             {},
	ast.IsIPv4Compat:       {},
	ast.IsIPv4Mapped:       {},
	ast.IsIPv6:             {},
	ast.JSONValid:          {},
	ast.RegexpLike:         {},
}