ddl: store default value as string when value type is binary or bit

[crazycs520]

What problem does this PR solve?

In v2.1.4, execute below SQL will be panic: v2.1.5 and after won't panic.

create table t (a int default b'0');
show columns from t;    # panic here

The main reason of panic is we think the ColumnInfo.DefaultValue is a string type( you can check the code of ColumnInfo.DefaultValue usage place ). but in upper SQL situation, the default value will be uint64, and after json Marshal and Unmarshal, the default value type will be float64. That's not what would expect.

Below was a simple example of json marshal and unmarshal:

package main

import (
	"encoding/json"
	"fmt"
	"reflect"
)

type Column struct {
	Default interface{} `json:"default"`
}

func main() {
	c := Column{
		Default: uint64(1),
	}
	data, _ := json.Marshal(c)
	c1 := Column{}
	json.Unmarshal(data, &c1)
	fmt.Printf("%v\n", reflect.TypeOf(c1.Default))    // the output is float64.
}

What is changed and how it works?

Change getDefaultValue function to convert uint64 to string before return.

Check List

Tests

• Unit test

Code changes

Side effects

Related changes

• Need to cherry-pick to the release branch

[crazycs520]

/run-all-tests

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@08346b7). Click here to learn what that means.
The diff coverage is 50%.

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[crazycs520]

/run-all-tests

[crazycs520]

/run-all-tests

[XuHuaiyu]

It seems that the default value is TypeBit, why won't it go through line 528?

[crazycs520]

The value type is typeBit, but the column type is Int.
eg: create table t (a int default b'1');

[winkyao]

LGTM

[zimulala]

LGTM

[XuHuaiyu]

LGTM