for _, v := range []byte(sql) {
			if v == '?' {
				if len(vars) > idx {
					newSQL.WriteString(vars[idx])
					idx++
					continue
				}
			}
			newSQL.WriteByte(v)
		}

		sql = newSQL.String()
	} else {
		sql = numericPlaceholder.ReplaceAllString(sql, "$$$1$$")

		sql = numericPlaceholderRe.ReplaceAllStringFunc(sql, func(v string) string {
			num := v[1 : len(v)-1]

		es                 = ExampleStruct{Name: "test", Val: "test"}
		intVal   intType   = 1
		floatVal floatType = 1.23
	)

	results := []struct {
		SQL           string
		NumericRegexp *regexp.Regexp
		Vars          []interface{}
		Result        string
	}{
		{
			SQL:           "create table users (name, age, height, actived, bytes, create_at, update_at, deleted_at, email, role, pass) values (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)",

# 异步 SQL 关系型数据库

**FastAPI** 使用 <a href="https://github.com/encode/databases" class="external-link" target="_blank">`encode/databases`</a> 为连接数据库提供异步支持（`async` 与 `await`）。

`databases` 兼容以下数据库：

* PostgreSQL
* MySQL
* SQLite

本章示例使用 **SQLite**，它使用的是单文件，且 Python 内置集成了 SQLite，因此，可以直接复制并运行本章示例。

生产环境下，则要使用 **PostgreSQL** 等数据库服务器。

!!! tip "提示"

Later, for your production application, you might want to use a database server like **PostgreSQL**.

!!! tip
    You could adopt ideas from the section about SQLAlchemy ORM ([SQL (Relational) Databases](../tutorial/sql-databases.md){.internal-link target=_blank}), like using utility functions to perform operations in the database, independent of your **FastAPI** code.

package gorm

import (
	"context"
	"database/sql"
	"database/sql/driver"
	"errors"
	"reflect"
	"sync"
)

type Stmt struct {
	*sql.Stmt
	Transaction bool
	prepared    chan struct{}
	prepareErr  error
}

type PreparedStmtDB struct {
	Stmts       map[string]*Stmt
	PreparedSQL []string
	Mux         *sync.RWMutex
	ConnPool
}

func NewPreparedStmtDB(connPool ConnPool) *PreparedStmtDB {

					if e, ok := v.Exprs[0].(Expr); ok {
						sql := strings.ToUpper(e.SQL)
						wrapInParentheses = strings.Contains(sql, AndWithSpace) || strings.Contains(sql, OrWithSpace)
					}
				}
			case AndConditions:
				if len(v.Exprs) == 1 {
					if e, ok := v.Exprs[0].(Expr); ok {
						sql := strings.ToUpper(e.SQL)
						wrapInParentheses = strings.Contains(sql, AndWithSpace) || strings.Contains(sql, OrWithSpace)
					}
				}
			case Expr:

	}

	for _, f := range p.fns {
		f(db)
	}

	if stmt.SQL.Len() > 0 {
		db.Logger.Trace(stmt.Context, curTime, func() (string, int64) {
			sql, vars := stmt.SQL.String(), stmt.Vars
			if filter, ok := db.Logger.(ParamsFilter); ok {
				sql, vars = filter.ParamsFilter(stmt.Context, stmt.SQL.String(), stmt.Vars...)
			}
			return db.Dialector.Explain(sql, vars...), db.RowsAffected
		}, db.Error)
	}

	Constraint string // length(phone) >= 10
	*Field
}

func (chk *CheckConstraint) GetName() string { return chk.Name }

func (chk *CheckConstraint) Build() (sql string, vars []interface{}) {
	return "CONSTRAINT ? CHECK (?)", []interface{}{clause.Column{Name: chk.Name}, clause.Expr{SQL: chk.Constraint}}
}

// ParseCheckConstraints parse schema check constraints
func (schema *Schema) ParseCheckConstraints() map[string]CheckConstraint {

package schema

import (
	"bytes"
	"context"
	"database/sql"
	"database/sql/driver"
	"encoding/gob"
	"encoding/json"
	"fmt"
	"reflect"
	"strings"
	"sync"
	"time"
)

var serializerMap = sync.Map{}

// RegisterSerializer register serializer
func RegisterSerializer(name string, serializer SerializerInterface) {
	serializerMap.Store(strings.ToLower(name), serializer)
}

// GetSerializer get serializer

					clause.And(clause.Expr{SQL: "`score` <= ?", Vars: []interface{}{100}, WithoutParentheses: false}))},
			}},
			"SELECT * FROM `users` WHERE (`users`.`id` <> ? AND NOT `score` <= ?)",
			[]interface{}{"1", 100},
		},
		{
			[]clause.Interface{clause.Select{}, clause.From{}, clause.Where{
				Exprs: []clause.Expression{clause.Not(clause.Expr{SQL: "`score` <= ?", Vars: []interface{}{100}},