Golang Column.HashCode方法代碼示例

// propagateConstant propagate constant values of equality predicates and inequality predicates in a condition.
func propagateConstant(conditions []expression.Expression) []expression.Expression {
	if len(conditions) == 0 {
		return conditions
	}
	// Propagate constants in equality predicates.
	// e.g. for condition: "a = b and b = c and c = a and a = 1";
	// we propagate constant as the following step:
	// first: "1 = b and b = c and c = 1 and a = 1";
	// next:  "1 = b and 1 = c and c = 1 and a = 1";
	// next:  "1 = b and 1 = c and 1 = 1 and a = 1";
	// next:  "1 = b and 1 = c and a = 1";

	// e.g for condition: "a = b and b = c and b = 2 and a = 1";
	// we propagate constant as the following step:
	// first: "a = 2 and 2 = c and b = 2 and a = 1";
	// next:  "a = 2 and 2 = c and b = 2 and 2 = 1";
	// next:  "0"
	isSource := make([]bool, len(conditions))
	type transitiveEqualityPredicate map[string]*expression.Constant // transitive equality predicates between one column and one constant
	for {
		equalities := make(transitiveEqualityPredicate, 0)
		for i, getOneEquality := 0, false; i < len(conditions) && !getOneEquality; i++ {
			if isSource[i] {
				continue
			}
			expr, ok := conditions[i].(*expression.ScalarFunction)
			if !ok {
				continue
			}
			// process the included OR conditions recursively to do the same for CNF item.
			switch expr.FuncName.L {
			case ast.OrOr:
				expressions := expression.SplitDNFItems(conditions[i])
				newExpression := make([]expression.Expression, 0)
				for _, v := range expressions {
					newExpression = append(newExpression, propagateConstant([]expression.Expression{v})...)
				}
				conditions[i] = expression.ComposeDNFCondition(newExpression)
				isSource[i] = true
			case ast.AndAnd:
				newExpression := propagateConstant(expression.SplitCNFItems(conditions[i]))
				conditions[i] = expression.ComposeCNFCondition(newExpression)
				isSource[i] = true
			case ast.EQ:
				var (
					col *expression.Column
					val *expression.Constant
				)
				leftConst, leftIsConst := expr.Args[0].(*expression.Constant)
				rightConst, rightIsConst := expr.Args[1].(*expression.Constant)
				leftCol, leftIsCol := expr.Args[0].(*expression.Column)
				rightCol, rightIsCol := expr.Args[1].(*expression.Column)
				if rightIsConst && leftIsCol {
					col = leftCol
					val = rightConst
				} else if leftIsConst && rightIsCol {
					col = rightCol
					val = leftConst
				} else {
					continue
				}
				equalities[string(col.HashCode())] = val
				isSource[i] = true
				getOneEquality = true
			}
		}
		if len(equalities) == 0 {
			break
		}
		for i := 0; i < len(conditions); i++ {
			if isSource[i] {
				continue
			}
			if len(equalities) != 0 {
				conditions[i] = constantSubstitute(equalities, conditions[i])
			}
		}
	}
	// Propagate transitive inequality predicates.
	// e.g for conditions "a = b and c = d and a = c and g = h and b > 0 and e != 0 and g like 'abc'",
	//     we propagate constant as the following step:
	// 1. build multiple equality predicates(mep):
	//    =(a, b, c, d), =(g, h).
	// 2. extract inequality predicates between one constant and one column,
	//    and rewrite them using the root column of a multiple equality predicate:
	//    b > 0, e != 0, g like 'abc' ==> a > 0, g like 'abc'.
	//    ATTENTION: here column 'e' doesn't belong to any mep, so we skip "e != 0".
	// 3. propagate constants in these inequality predicates, and we finally get:
	//    "a = b and c = d and a = c and e = f and g = h and e != 0 and a > 0 and b > 0 and c > 0 and d > 0 and g like 'abc' and h like 'abc' ".
	multipleEqualities := make(map[*expression.Column]*expression.Column, 0)
	for _, cond := range conditions { // build multiple equality predicates.
		expr, ok := cond.(*expression.ScalarFunction)
		if ok && expr.FuncName.L == ast.EQ {
			left, ok1 := expr.Args[0].(*expression.Column)
			right, ok2 := expr.Args[1].(*expression.Column)
			if ok1 && ok2 {
				UnionColumns(left, right, multipleEqualities)
			}
		}
//.........這裏部分代碼省略.........