sql常用语句
创建表
CREATE TABLE IF NOT EXISTS "T_Person" ( "id" INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT, "name" TEXT, "age" INTEGER, "heigth" REAL)//下边是sqllite编译器里边的语句/*简单约束*/CREATE TABLE IF NOT EXISTS t_student( id INTEGER PRIMARY KEY AUTOINCREMENT, name TEXT, age INTEGER);CREATE TABLE IF NOT EXISTS t_student( id INTEGER PRIMARY KEY AUTOINCREMENT, name TEXT UNIQUE, age INTEGER);/*添加主键*/CREATE TABLE IF NOT EXISTS t_student( id INTEGER PRIMARY KEY AUTOINCREMENT, name TEXT, age INTEGER, score REAL);/*添加主键*/CREATE TABLE IF NOT EXISTS t_student( id INTEGER, name TEXT, age INTEGER, score REAL, PRIMARY KEY(id));
查询
/*分页*/ SELECT * FROM t_student ORDER BY id ASC LIMIT 30, 10; /*排序*/ SELECT * FROM t_student WHERE score > 50 ORDER BY age DESC; SELECT * FROM t_student WHERE score < 50 ORDER BY age ASC , score DESC; /*计量*/ SELECT COUNT(*) FROM t_student WHERE age > 50; /*别名*/ SELECT name as myName, age as myAge, score as myScore FROM t_student; SELECT name myName, age myAge, score myScore FROM t_student; SELECT s.name myName, s.age myAge, s.score myScore FROM t_student s WHERE s.age > 50; /*查询*/ SELECT name, age, score FROM t_student; SELECT * FROM t_student;
修改
UPDATE t_student SET name = 'MM' WHERE age = 10; UPDATE t_student SET name = 'WW' WHERE age is 7; UPDATE t_student SET name = 'XXOO' WHERE age < 20; UPDATE t_student SET name = 'NNMM' WHERE age < 50 and score > 10; /*更新记录的name*/ UPDATE t_student SET name = 'zhangsan';
删除
DELETE FROM t_student; DELETE FROM t_student WHERE age < 50;
插入
INSERT INTO t_student (age, score, name) VALUES ('28', 100, 'zhangsan'); INSERT INTO t_student (name, age) VALUES ('lisi', '28'); INSERT INTO t_student (score) VALUES (100);
删除表
/*删除表*/ DROP TABLE IF EXISTS t_student;
FMDB
-
什么是FMDB
FMDB是iOS平台的SQLite数据库框架 FMDB以OC的方式封装了SQLite的C语言API -
FMDB的优点
使用起来更加面向对象，省去了很多麻烦、冗余的C语言代码 对比苹果自带的Core Data框架，更加轻量级和灵活 提供了多线程安全的数据库操作方法，有效地防止数据混乱 -
FMDB 的github地址
-
FMDB有三个主要的类
FMDatabase一个FMDatabase对象就代表一个单独的SQLite数据库
用来执行SQL语句
-
FMResultSet
使用FMDatabase执行查询后的结果集 -
FMDatabaseQueue
用于在多线程中执行多个查询或更新，它是线程安全的
通过指定SQLite数据库文件路径来创建FMDatabase对象 FMDatabase *db = [FMDatabase databaseWithPath:path]; if (![db open]) { NSLog(@"数据库打开失败！"); } 文件路径有三种情况 具体文件路径 如果不存在会自动创建 空字符串@"" 会在临时目录创建一个空的数据库 当FMDatabase连接关闭时，数据库文件也被删除 在FMDB中，除查询以外的所有操作，都称为“更新” create、drop、insert、update、delete等 使用executeUpdate:方法执行更新 - (BOOL)executeUpdate:(NSString*)sql, ... - (BOOL)executeUpdateWithFormat:(NSString*)format, ... - (BOOL)executeUpdate:(NSString*)sql withArgumentsInArray:(NSArray *)arguments 示例 [db executeUpdate:@"UPDATE t_student SET age = ? WHERE name = ?;", @20, @"Jack"]
查询的方法
查询方法 - (FMResultSet *)executeQuery:(NSString*)sql, ... - (FMResultSet *)executeQueryWithFormat:(NSString*)format, ... - (FMResultSet *)executeQuery:(NSString *)sql withArgumentsInArray:(NSArray *)arguments 示例 // 查询数据 FMResultSet *rs = [db executeQuery:@"SELECT * FROM t_student"]; // 遍历结果集 while ([rs next]) { NSString *name = [rs stringForColumn:@"name"]; int age = [rs intForColumn:@"age"]; double score = [rs doubleForColumn:@"score"]; }
FMDatabaseQueue
-
FMDatabase这个类是线程不安全的，如果在多个线程同时使用一个FMDatabase实例,会造成数据混乱问题
-
为了保证线程安全,FMDB提供方便快捷的FMDatabaseQueue类
-
FMDatabaseQueue 的创建
FMDatabaseQueue *queue = [FMDatabaseQueue databaseQueueWithPath:path];
简单使用 [queue inDatabase:^(FMDatabase *db) { [db executeUpdate:@"INSERT INTO t_student(name) VALUES (?)", @"Jack"]; [db executeUpdate:@"INSERT INTO t_student(name) VALUES (?)", @"Rose"]; [db executeUpdate:@"INSERT INTO t_student(name) VALUES (?)", @"Jim"]; FMResultSet *rs = [db executeQuery:@"select * from t_student"]; while ([rs next]) { // … } }];
使用事务
[queue inTransaction:^(FMDatabase *db, BOOL *rollback) { [db executeUpdate:@"INSERT INTO t_student(name) VALUES (?)", @"Jack"]; [db executeUpdate:@"INSERT INTO t_student(name) VALUES (?)", @"Rose"]; [db executeUpdate:@"INSERT INTO t_student(name) VALUES (?)", @"Jim"]; FMResultSet *rs = [db executeQuery:@"select * from t_student"]; while ([rs next]) { // … } }]; 事务回滚 *rollback = YES; 总结：本博客主要学习了sql增删改查语句，学习了FMDB的框架的三个类: FMDatabase对象就代表一个单独的SQLite数据库,FMDatabase执行查询后的结果集,FMDatabaseQueued串行队列，同步任务;