// The return type of a CASE expression is the compatible aggregated type of all return values,
// but also depends on the context in which it is used.
// If used in a string context, the result is returned as a string.
// If used in a numeric context, the result is returned as a decimal, real, or integer value.
func (v *typeInferrer) handleCaseExpr(x *ast.CaseExpr) {
var currType *types.FieldType
for _, w := range x.WhenClauses {
t := w.Result.GetType()
if currType == nil {
currType = t
continue
}
mtp := types.MergeFieldType(currType.Tp, t.Tp)
if mtp == t.Tp && mtp != currType.Tp {
currType.Charset = t.Charset
currType.Collate = t.Collate
}
currType.Tp = mtp
}
if x.ElseClause != nil {
t := x.ElseClause.GetType()
if currType == nil {
currType = t
} else {
mtp := types.MergeFieldType(currType.Tp, t.Tp)
if mtp == t.Tp && mtp != currType.Tp {
currType.Charset = t.Charset
currType.Collate = t.Collate
}
currType.Tp = mtp
}
}
x.SetType(currType)
// TODO: We need a better way to set charset/collation
x.Type.Charset, x.Type.Collate = types.DefaultCharsetForType(x.Type.Tp)
}
// ProtoColumnsToFieldTypes converts tipb column info slice to FieldTyps slice.
func ProtoColumnsToFieldTypes(pColumns []*tipb.ColumnInfo) []*types.FieldType {
fields := make([]*types.FieldType, len(pColumns))
for i, v := range pColumns {
field := new(types.FieldType)
field.Tp = byte(v.GetTp())
field.Collate = mysql.Collations[byte(v.GetCollation())]
field.Decimal = int(v.GetDecimal())
field.Flen = int(v.GetColumnLen())
field.Flag = uint(v.GetFlag())
field.Elems = v.GetElems()
fields[i] = field
}
return fields
}