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sql/(analyzer,parse,expression): implement case expression #576
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,188 @@ | ||
| package expression | ||
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| import ( | ||
| "bytes" | ||
|
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| "gopkg.in/src-d/go-mysql-server.v0/sql" | ||
| ) | ||
|
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||
| // CaseBranch is a single branch of a case expression. | ||
| type CaseBranch struct { | ||
| Cond sql.Expression | ||
| Value sql.Expression | ||
| } | ||
|
|
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| // Case is an expression that returns the value of one of its branches when a | ||
| // condition is met. | ||
| type Case struct { | ||
| Expr sql.Expression | ||
| Branches []CaseBranch | ||
| Else sql.Expression | ||
| } | ||
|
|
||
| // NewCase returns an new Case expression. | ||
| func NewCase(expr sql.Expression, branches []CaseBranch, elseExpr sql.Expression) *Case { | ||
| return &Case{expr, branches, elseExpr} | ||
| } | ||
|
|
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| // Type implements the sql.Expression interface. | ||
| func (c *Case) Type() sql.Type { | ||
| for _, b := range c.Branches { | ||
| return b.Value.Type() | ||
| } | ||
| return c.Else.Type() | ||
| } | ||
|
|
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| // IsNullable implements the sql.Expression interface. | ||
| func (c *Case) IsNullable() bool { | ||
| for _, b := range c.Branches { | ||
| if b.Value.IsNullable() { | ||
| return true | ||
| } | ||
| } | ||
|
|
||
| return c.Else == nil || c.Else.IsNullable() | ||
| } | ||
|
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| // Resolved implements the sql.Expression interface. | ||
| func (c *Case) Resolved() bool { | ||
| if (c.Expr != nil && !c.Expr.Resolved()) || | ||
| (c.Else != nil && !c.Else.Resolved()) { | ||
| return false | ||
| } | ||
|
|
||
| for _, b := range c.Branches { | ||
| if !b.Cond.Resolved() || !b.Value.Resolved() { | ||
| return false | ||
| } | ||
| } | ||
|
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| return true | ||
| } | ||
|
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| // Children implements the sql.Expression interface. | ||
| func (c *Case) Children() []sql.Expression { | ||
| var children []sql.Expression | ||
|
|
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| if c.Expr != nil { | ||
| children = append(children, c.Expr) | ||
| } | ||
|
|
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| for _, b := range c.Branches { | ||
| children = append(children, b.Cond, b.Value) | ||
| } | ||
|
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| if c.Else != nil { | ||
| children = append(children, c.Else) | ||
| } | ||
|
|
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| return children | ||
| } | ||
|
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| // Eval implements the sql.Expression interface. | ||
| func (c *Case) Eval(ctx *sql.Context, row sql.Row) (interface{}, error) { | ||
| span, ctx := ctx.Span("expression.Case") | ||
| defer span.Finish() | ||
|
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||
| var expr interface{} | ||
| var err error | ||
| if c.Expr != nil { | ||
| expr, err = c.Expr.Eval(ctx, row) | ||
| if err != nil { | ||
| return nil, err | ||
| } | ||
| } | ||
|
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||
| for _, b := range c.Branches { | ||
| var cond sql.Expression | ||
| if expr != nil { | ||
| cond = NewEquals(NewLiteral(expr, c.Expr.Type()), b.Cond) | ||
| } else { | ||
| cond = b.Cond | ||
| } | ||
|
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| v, err := cond.Eval(ctx, row) | ||
| if err != nil { | ||
| return nil, err | ||
| } | ||
|
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| v, err = sql.Boolean.Convert(v) | ||
| if err != nil { | ||
| return nil, err | ||
| } | ||
|
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| if v == true { | ||
| return b.Value.Eval(ctx, row) | ||
| } | ||
| } | ||
|
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| if c.Else != nil { | ||
| return c.Else.Eval(ctx, row) | ||
| } | ||
|
|
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| return nil, nil | ||
| } | ||
|
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| // TransformUp implements the sql.Expression interface. | ||
| func (c *Case) TransformUp(f sql.TransformExprFunc) (sql.Expression, error) { | ||
| var expr sql.Expression | ||
| var err error | ||
|
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| if c.Expr != nil { | ||
| expr, err = c.Expr.TransformUp(f) | ||
| if err != nil { | ||
| return nil, err | ||
| } | ||
| } | ||
|
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| var branches []CaseBranch | ||
| for _, b := range c.Branches { | ||
| var nb CaseBranch | ||
|
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| nb.Cond, err = b.Cond.TransformUp(f) | ||
| if err != nil { | ||
| return nil, err | ||
| } | ||
|
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| nb.Value, err = b.Value.TransformUp(f) | ||
| if err != nil { | ||
| return nil, err | ||
| } | ||
|
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| branches = append(branches, nb) | ||
| } | ||
|
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| var elseExpr sql.Expression | ||
| if c.Else != nil { | ||
| elseExpr, err = c.Else.TransformUp(f) | ||
| if err != nil { | ||
| return nil, err | ||
| } | ||
| } | ||
|
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| return f(NewCase(expr, branches, elseExpr)) | ||
| } | ||
|
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| func (c *Case) String() string { | ||
| var buf bytes.Buffer | ||
|
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| buf.WriteString("CASE ") | ||
| if c.Expr != nil { | ||
| buf.WriteString(c.Expr.String()) | ||
| } | ||
|
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| for _, b := range c.Branches { | ||
| buf.WriteString(" WHEN ") | ||
| buf.WriteString(b.Cond.String()) | ||
| buf.WriteString(" THEN ") | ||
| buf.WriteString(b.Value.String()) | ||
| } | ||
|
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| if c.Else != nil { | ||
| buf.WriteString(" ELSE ") | ||
| buf.WriteString(c.Else.String()) | ||
| } | ||
|
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| buf.WriteString(" END") | ||
| return buf.String() | ||
| } |
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Just open question - doesn't make sense as a optimization to squash some rules?
For instance instead of 3 times looping, we may have one loop with some cases - loud thinking.
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this query phase is really fast compared with the rest. The idea of having separated rules is the synergy that we can obtain executing them again and again, interacting with other rules.