planner/

Example planner usage

There are two execution paths in tidb build physical plan from ast node

1. AST -> Physical Plan Step-by-step through multiple functions

    ```go
    import (
    plannercore "github.com/pingcap/tidb/planner/core"
    )
   
    func main() {
    stmts, _, err := parser.Parse(SQL_STRING)
    is := getInfoSchema()
    logical_plan, _, err := plannercore.BuildLogicalPlan(stmts[0], is)
    physical_plan, err = plannercore.DoOptimize(
            context.TODO(),
            flagPredicatePushDown|flagDecorrelate|flagPrunColumns,
            logical_plan.(LogicalPlan))
    }
    ```
   

2. AST -> Physical Plan in one function (AST -> logical plan -> optimize -> physical plan)

    ```go
    import (
    "github.com/pingcap/tidb/planner"
    )
   
    func main() {
    stmts, _, err := parser.Parse(SQL_STRING)
    is := getInfoSchema()
    physical_plan, _, err := planner.Optimize(
            context.TODO(),
            sessionctx.Context,
            stmts[0],
            is)
    }
    ```
   

So, there are several entry functions in planner

1. In planner/optimize.go

    ```go
    func Optimize(
            ctx context.Context,
            sctx sessionctx.Context,
            node ast.Node,
            is infoschema.InfoSchema) (plannercore.Plan, types.NameSlice, error)
    ```
   

2. In planner/core/planbuilder.go

    ```go
    func (b *PlanBuilder) Build(
            ctx context.Context,
            node ast.Node) (Plan, error) // Returns LogicalPlan
    ```
   

3. In planner/core/optimizer.go

    ```go
    func DoOptimize(
            ctx context.Context,
            flag uint64,
            logic LogicalPlan) (PhysicalPlan, float64, error)
    ```
   

4. In planner/core/optimizer.go

    ```go
    func BuildLogicalPlan(
            ctx context.Context,
            sctx sessionctx.Context,
            node ast.Node,
            is infoschema.InfoSchema) (Plan, types.NameSlice, error) // Also returns LogicalPlan.
    {
            // Simply invokes Build() function above in 2
    }
    ```