[在Clickhouse的十进制列(Decimal(12,4))中保存值(0.0003)时,保存的值为0.0002。为什么表现得如此?但是当我直接通过SQL插入时,我能够毫无问题地保存它。这意味着我编写的go程序是错误的?
■创建表
CREATE TABLE test_ch (
id Decimal(12,4),
created_at DateTime
) ENGINE = MergeTree() PARTITION BY toYYYYMMDD(created_at) ORDER BY (created_at);
■来源
import (
"database/sql"
"fmt"
"time"
"github.com/ClickHouse/clickhouse-go"
sq "github.com/Masterminds/squirrel"
)
var ConnectCH *sql.DB
func main() {
SetClickHouse()
insert()
}
func insert() error {
return Exec(func(tx *sql.Tx) error {
prepare, _, _ := sq.Insert("test_ch").
Columns(
"id",
"created_at",
).Values().ToSql()
stmt, _ := tx.Prepare(prepare)
createdAt := time.Now().Format("2006-01-02 15:04:05")
if _, err := stmt.Exec(
0.0003,
createdAt,
); err != nil {
return err
}
return nil
})
}
func recoverAndRollback(tx *sql.Tx) {
if r := recover(); r != nil {
tx.Rollback()
}
}
func Exec(t func(*sql.Tx) error) error {
tx, err := ConnectCH.Begin()
if err != nil {
tx.Rollback()
return err
}
defer recoverAndRollback(tx)
if err := t(tx); err != nil {
tx.Rollback()
return err
}
if err := tx.Commit(); err != nil {
tx.Rollback()
return err
}
return nil
}
func SetClickHouse() error {
var err error
url := fmt.Sprintf("tcp://%s:%s", "clickhouse", "9000")
ConnectCH, err = sql.Open("clickhouse", url)
if err != nil {
return err
}
if err := ConnectCH.Ping(); err != nil {
if exception, ok := err.(*clickhouse.Exception); ok {
fmt.Printf("[%d] %s \n%s\n", exception.Code, exception.Message, exception.StackTrace)
} else {
fmt.Println(err)
}
return err
}
return nil
}
■输出
当id = 0.0001时SELECT *
FROM test_ch
┌─────id─┬──────────created_at─┐
│ 0.0001 │ 2020-01-09 01:58:49 │
└────────┴─────────────────────┘
没问题
当id = 0.0002时SELECT *
FROM test_ch
┌─────id─┬──────────created_at─┐
│ 0.0002 │ 2020-01-09 01:59:33 │
└────────┴─────────────────────┘
没问题
当id = 0.0003时SELECT *
FROM test_ch
┌─────id─┬──────────created_at─┐
│ 0.0002 │ 2020-01-09 02:00:30 │
└────────┴─────────────────────┘
为什么是0.0002?
性能
SELECT CAST(toFloat64('0.0003'), 'Decimal(12, 8)')
┌─CAST(toFloat64('0.0003'), 'Decimal(12, 8)')─┐
│ 0.00029999 │
└─────────────────────────────────────────────┘
SELECT CAST('0.0003', 'Decimal(12, 8)')
┌─CAST('0.0003', 'Decimal(12, 8)')─┐
│ 0.00030000 │
└──────────────────────────────────┘