// Copyright 2020 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, // See the License for the specific language governing permissions and // limitations under the License. package expression import ( "strings" "github.com/pingcap/parser/ast" "github.com/pingcap/parser/charset" "github.com/pingcap/tidb/sessionctx" "github.com/pingcap/tidb/types" ) type collationInfo struct { coer Coercibility coerInit bool charset string collation string flen int } func (c *collationInfo) HasCoercibility() bool { return c.coerInit } func (c *collationInfo) Coercibility() Coercibility { return c.coer } // SetCoercibility implements CollationInfo SetCoercibility interface. func (c *collationInfo) SetCoercibility(val Coercibility) { c.coer = val c.coerInit = true } func (c *collationInfo) SetCharsetAndCollation(chs, coll string) { c.charset, c.collation = chs, coll } func (c *collationInfo) CharsetAndCollation(ctx sessionctx.Context) (string, string) { if c.charset != "" || c.collation != "" { return c.charset, c.collation } if ctx != nil && ctx.GetSessionVars() != nil { c.charset, c.collation = ctx.GetSessionVars().GetCharsetInfo() } if c.charset == "" || c.collation == "" { c.charset, c.collation = charset.GetDefaultCharsetAndCollate() } c.flen = types.UnspecifiedLength return c.charset, c.collation } // CollationInfo contains all interfaces about dealing with collation. type CollationInfo interface { // HasCoercibility returns if the Coercibility value is initialized. HasCoercibility() bool // Coercibility returns the coercibility value which is used to check collations. Coercibility() Coercibility // SetCoercibility sets a specified coercibility for this expression. SetCoercibility(val Coercibility) // CharsetAndCollation ... CharsetAndCollation(ctx sessionctx.Context) (string, string) // SetCharsetAndCollation ... SetCharsetAndCollation(chs, coll string) } // Coercibility values are used to check whether the collation of one item can be coerced to // the collation of other. See https://dev.mysql.com/doc/refman/8.0/en/charset-collation-coercibility.html type Coercibility int const ( // CoercibilityExplicit is derived from an explicit COLLATE clause. CoercibilityExplicit Coercibility = 0 // CoercibilityNone is derived from the concatenation of two strings with different collations. CoercibilityNone Coercibility = 1 // CoercibilityImplicit is derived from a column or a stored routine parameter or local variable. CoercibilityImplicit Coercibility = 2 // CoercibilitySysconst is derived from a “system constant” (the string returned by functions such as USER() or VERSION()). CoercibilitySysconst Coercibility = 3 // CoercibilityCoercible is derived from a literal. CoercibilityCoercible Coercibility = 4 // CoercibilityNumeric is derived from a numeric or temporal value. CoercibilityNumeric Coercibility = 5 // CoercibilityIgnorable is derived from NULL or an expression that is derived from NULL. CoercibilityIgnorable Coercibility = 6 ) var ( sysConstFuncs = map[string]struct{}{ ast.User: {}, ast.Version: {}, ast.Database: {}, ast.CurrentRole: {}, ast.CurrentUser: {}, } // collationPriority is the priority when infer the result collation, the priority of collation a > b iff collationPriority[a] > collationPriority[b] collationPriority = map[string]int{ charset.CollationASCII: 0, charset.CollationLatin1: 1, "utf8_general_ci": 2, charset.CollationUTF8: 3, "utf8mb4_general_ci": 4, charset.CollationUTF8MB4: 5, charset.CollationBin: 6, } // CollationStrictness indicates the strictness of comparison of the collation. The unequal order in a weak collation also holds in a strict collation. // For example, if a < b in a weak collation(e.g. general_ci), then there must be a < b in a strict collation(e.g. _bin). CollationStrictness = map[string]int{ "utf8_general_ci": 0, "utf8mb4_general_ci": 0, charset.CollationASCII: 1, charset.CollationLatin1: 1, charset.CollationUTF8: 1, charset.CollationUTF8MB4: 1, charset.CollationBin: 2, } ) func deriveCoercibilityForScarlarFunc(sf *ScalarFunction) Coercibility { if _, ok := sysConstFuncs[sf.FuncName.L]; ok { return CoercibilitySysconst } if sf.RetType.EvalType() != types.ETString { return CoercibilityNumeric } coer := CoercibilityIgnorable for _, arg := range sf.GetArgs() { if arg.Coercibility() < coer { coer = arg.Coercibility() } } return coer } func deriveCoercibilityForConstant(c *Constant) Coercibility { if c.Value.IsNull() { return CoercibilityIgnorable } else if c.RetType.EvalType() != types.ETString { return CoercibilityNumeric } return CoercibilityCoercible } func deriveCoercibilityForColumn(c *Column) Coercibility { if c.RetType.EvalType() != types.ETString { return CoercibilityNumeric } return CoercibilityImplicit } // DeriveCollationFromExprs derives collation information from these expressions. func DeriveCollationFromExprs(ctx sessionctx.Context, exprs ...Expression) (dstCharset, dstCollation string) { curCoer := CoercibilityCoercible curCollationPriority := -1 dstCharset, dstCollation = charset.GetDefaultCharsetAndCollate() if ctx != nil && ctx.GetSessionVars() != nil { dstCharset, dstCollation = ctx.GetSessionVars().GetCharsetInfo() if dstCharset == "" || dstCollation == "" { dstCharset, dstCollation = charset.GetDefaultCharsetAndCollate() } } hasStrArg := false // see https://dev.mysql.com/doc/refman/8.0/en/charset-collation-coercibility.html for _, e := range exprs { if e.GetType().EvalType() != types.ETString { continue } hasStrArg = true coer := e.Coercibility() ft := e.GetType() collationPriority, ok := collationPriority[strings.ToLower(ft.Collate)] if !ok { collationPriority = -1 } if coer != curCoer { if coer < curCoer { curCoer, curCollationPriority, dstCharset, dstCollation = coer, collationPriority, ft.Charset, ft.Collate } continue } if !ok || collationPriority <= curCollationPriority { continue } curCollationPriority, dstCharset, dstCollation = collationPriority, ft.Charset, ft.Collate } if !hasStrArg { dstCharset, dstCollation = charset.CharsetBin, charset.CollationBin } return }