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表达式函数

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2881099 edited this page Aug 8, 2024 · 76 revisions

这是 FreeSql 非常特色的功能之一，深入细化函数解析，所支持的类型基本都可以使用对应的表达式函数，例如 日期、字符串、IN查询、数组（PostgreSQL的数组）、字典（PostgreSQL HStore)等等。

动态Lambda表达式

示例

Expression<Func<T, bool>> where = null;
where = where.And(b => b.num > 0);
where = where.Or(b => b.num > 0);
fsql.Select<T>().Where(where);

In查询

fsql.Select<T>()
  .Where(a => new[] { 1, 2, 3 }.Contains(a.Id))
  .ToList();
//SELECT .. FROM ..
//WHERE (a.`Id` in (1,2,3))

已优化，防止 where in 元素多过的 SQL 错误，如：

[Err] ORA-01795: maximum number of expressions in a list a 1000

原来：where id in (1..1333)

现在：where id in (1..500) or id in (501..1000) or id in (1001..1333)

In多列查询

//元组集合
vae lst = new List<(Guid, DateTime)>();
lst.Add((Guid.NewGuid(), DateTime.Now));
lst.Add((Guid.NewGuid(), DateTime.Now));

var t2 = fsql.Select<T>()
  .Where(a => lst.Contains(a.Id, a.ct1))
  .ToList();
//SELECT .. FROM ..
//WHERE (a."Id" = '685ee1f6-bdf6-4719-a291-c709b8a1378f' AND a."ct1" = '2019-12-07 23:55:27' OR 
//a."Id" = '5ecd838a-06a0-4c81-be43-1e77633b7404' AND a."ct1" = '2019-12-07 23:55:27')

v3.2.650 使用 .Where(a => list.Any(b => b.Item1 == a.Id && b.Item2 == a.ct1))

WHERE (id, code) in ((1,'code1'), (2,'code2')) 实现代码：https://github.com/2881099/FreeSql/issues/243

In子表

fsql.Select<Topic>()
  .Where(a => fsql.Select<Topic>().As("b").ToList(b => b.Id).Contains(a.Id))
  .ToList();
//SELECT a.`Id`, a.`Title`, a.`Clicks`, a.`CreateTime`, a.`CategoryId`
//FROM `Topic` a
//WHERE (((a.`Id`) in (SELECT b.`Id`
//    FROM `Topic` b)))

Exists子表

fsql.Select<Topic>()
  .Where(a => fsql.Select<Topic>().As("b").Where(b => b.Id == a.Id).Any())
  .ToList();
//SELECT a.`Id`, a.`Title`, a.`Clicks`, a.`CreateTime`, a.`CategoryId`
//FROM `Topic` a
//WHERE (exists(SELECT 1
//    FROM `Topic` b
//    WHERE (b.`Id` = a.`Id`)
//    limit 0,1))

查找今天创建的数据

fsql.Select<T>()
  .Where(a => a.CreateTime.Date == DateTime.Today)
  .ToList();
//这行代码说明 FreeSql 表达式解析强大，不是所有 ORM 都支持

fsql.Select<T>()
  .Where(a => a.CreateTime.Between(DateTime.Today, DateTime.Today.AddDays(1)))
  .ToList();
//正常用法应该是这样

SqlServer nvarchar/varchar 已兼容表达式解析，分别解析为：N'' 和 ''，优化索引执行计划；

日期格式化

fsql.Select<T>()
  .First(a => a.CreateTime.ToString("HH:mm:ss");
// SELECT date_format(a.`CreateTime`, '%H:%i:%s') as1 
// FROM `xxx` a 
// limit 0,1

v1.5.0 支持了常用 c# 日期格式化，yyyy MM dd HH mm ss yy M d H hh h m s tt t

tt t 为 AM PM

开窗函数

fsql.Select<T1, T2>()
  .InnerJoin((a, b) => b.Id == a.Id)
  .ToList((a, b) => new
  {
    Id = a.Id,
    EdiId = b.Id,
    over1 = SqlExt.Rank().Over().OrderBy(a.Id).OrderByDescending(b.EdiId).ToValue()
  });

v1.6.0 利用自定义解析功能，增加 SqlExt.Rank().Over().PartitionBy(...)、MySql group_concat 常用函数，欢迎 PR 补充

子表Exists

fsql.Select<Topic>()
  .Where(a => fsql.Select<Topic>().As("b").Where(b => b.Id == a.Id).Any())
  .ToList();
//SELECT a.`Id`, a.`Title`, a.`Clicks`, a.`CreateTime`, a.`CategoryId`
//FROM `Topic` a
//WHERE (exists(SELECT 1
//    FROM `Topic` b
//    WHERE (b.`Id` = a.`Id`)
//    limit 0,1))

提示：由于子查询的实体类与上层相同，使用 As("b") 指明别名，以便区分

子表In

fsql.Select<Topic>()
  .Where(a => fsql.Select<Topic>().As("b").ToList(b => b.Id).Contains(a.Id))
  .ToList();
//SELECT a.`Id`, a.`Title`, a.`Clicks`, a.`CreateTime`, a.`CategoryId`
//FROM `Topic` a
//WHERE (((a.`Id`) in (SELECT b.`Id`
//    FROM `Topic` b)))

子表Join

v1.8.0+ string.Join + ToList 实现将子查询的多行结果，拼接为一个字符串，如："1,2,3,4"

fsql.Select<Topic>().ToList(a => new {
  id = a.Id,
  concat = string.Join(",", fsql.Select<StringJoin01>().ToList(b => b.Id))
});
//SELECT a.`Id`, (SELECT group_concat(b.`Id` separator ',') 
//    FROM `StringJoin01` b) 
//FROM `Topic` a

提示：子查询 string.Join + ToList 适配了 sqlserver/pgsql/oracle/mysql/sqlite/firebird/达梦/金仓/南大/翰高 #405

子表First/Count/Sum/Max/Min/Avg

fsql.Select<Category>().ToList(a => new  {
  all = a,
  first = fsql.Select<Topic>().Where(b => b.CategoryId == a.Id).First(b => b.Id),
  count = fsql.Select<Topic>().Where(b => b.CategoryId == a.Id).Count(),
  sum = fsql.Select<Topic>().Where(b => b.CategoryId == a.Id).Sum(b => b.Clicks),
  max = fsql.Select<Topic>().Where(b => b.CategoryId == a.Id).Max(b => b.Clicks),
  min = fsql.Select<Topic>().Where(b => b.CategoryId == a.Id).Min(b => b.Clicks),
  avg = fsql.Select<Topic>().Where(b => b.CategoryId == a.Id).Avg(b => b.Clicks)
});

子表ToList

v3.2.650+ 以下最多执行3次 SQL

fsql.Select<Topic>().ToList(a => new
{
  all = a,
  list1 = fsql.Select<T2>().ToList(),
  list2 = fsql.Select<T2>().Where(b => b.TopicId == a.Id).ToList()
});

fsql.Select<Topic>()
  .GroupBy(a => new { a.Author })
  .WithTempQuery(a => new { Author = a.Key.Author, Count = a.Count() })
  .ToList(a => new {
    a.Author, a.Count,
    list1 = fsql.Select<T2>().ToList(),
    list2 = fsql.Select<T2>().Where(b => b.Author == a.Author).ToList()
  });

自定义解析

[ExpressionCall]
public static class DbFunc {
  //必要定义 static + ThreadLocal
  static ThreadLocal<ExpressionCallContext> context = new ThreadLocal<ExpressionCallContext>();

  public static DateTime FormatDateTime(this DateTime that, string arg1)
  {
    var up = context.Value;
    if (up.DataType == FreeSql.DataType.Sqlite) //重写内容
      up.Result = $"date_format({up.ParsedContent["that"]}, {up.ParsedContent["arg1"]})";
    return that;
  }
}

var sql1 = fsql.Select<SysModule>()
  .ToSql(a => a.CreateTime.FormatDateTime("yyyy-MM-dd"));
//SELECT date_format(a."CreateTime", 'yyyy-MM-dd') as1 
//FROM "SysModule" a

[ExpressionCall] 特性可在静态扩展类上标记，也可以在单个静态方法上标记；

ExpressionCallContext 属性 类型 描述
DataType FreeSql.DataType 用于实现不同数据库的适配判断条件
ParsedContent Dictionary<string, string> 函数的各参数解析结果
DbParameter DbParameter that 被参数化的对象（有可能为 null)
UserParameters List<DbParameter> 可附加参数化对象
Result string 返回表达式函数表示的 SQL 字符串

当扩展方法返回值为 string 时，其返回值也可以当作 context.Value.Result 功能

当不想解析指定参数时，使用特性 [RawValue] 标记

参数化

Where(lambda) 解析出来的默认是纯文本（已防止SQL注入），对数据库执行计划要求特别高，可以开启 lambda 参数化功能。

var fsql = new FreeSqlBuilder() //请务必定义成 Singleton 单例模式
  .UseGenerateCommandParameterWithLambda(true)
  ...

var id = 1;
fsql.Select<Song>().Where(a => a.Id == id).ToList();
//SELECT .. FROM `Song` a WHERE `Id` = @exp_0

生成的参数对象，DbType、Size、Precision、Scale 值设置默认已作优化，与实体属性定义一致。

诡异操作：

如果不希望 string 参数与实体属性的 Size 相同，可利用自定义表达式函数功能，如下：

var name = "testname";
fsql.Select<TestMySqlStringIsNullable>()
  .Where(a => a.varchar == name).ToList();

fsql.Select<TestMySqlStringIsNullable>()
  .Where(a => a.varchar == name.SetDbParameter(10)).ToList();

public class TestMySqlStringIsNullable {
  public Guid id { get; set; }

  [Column(DbType = "varchar(100)")]
  public string varchar { get; set; }
}

[ExpressionCall]
public static class DbFunc {
  static ThreadLocal<ExpressionCallContext> context = new ThreadLocal<ExpressionCallContext>();

  public static string SetDbParameter(this string that, int size)
  {
    if (context.Value.DbParameter != null)
      context.Value.DbParameter.Size = size;
    return context.Value.ParsedContent["that"];
  }
}

第一条语句产生的参数对象 Size 为 100，第二条为 10：

image

表达式函数全览

表达式 MySql SqlServer PostgreSQL Oracle 功能说明
a ? b : c case when a then b else c end case when a then b else c end case when a then b else c end case when a then b else c end a成立时取b值，否则取c值
a ?? b ifnull(a, b) isnull(a, b) coalesce(a, b) nvl(a, b) 当a为null时，取b值
数字 + 数字 a + b a + b a + b a + b 数字相加
数字 + 字符串 concat(a, b) cast(a as varchar) + cast(b as varchar) case(a as varchar)|| b a|| b 字符串相加，a或b任意一个为字符串时
a - b a - b a - b a - b a - b 减
a * b a * b a * b a * b a * b 乘
a / b a / b a / b a / b a / b 除
a / b a div b a / b a / b trunc(a / b) 整除(a,b都为整数)
a % b a % b a % b a % b mod(a,b) 模

等等...

数组

表达式 MySql SqlServer PostgreSQL Oracle 功能说明
a.Length - - case when a is null then 0 else array_length(a,1) end - 数组长度
常量数组.Length - - array_length(array[常量数组元素逗号分割],1) - 数组长度
a.Any() - - case when a is null then 0 else array_length(a,1) end > 0 - 数组是否为空
常量数组.Contains(b) b in (常量数组元素逗号分割) b in (常量数组元素逗号分割) b in (常量数组元素逗号分割) b in (常量数组元素逗号分割) IN查询
a.Contains(b) - - a @> array[b] - a数组是否包含b元素
a.Concat(b) - - a || b - 数组相连
a.Count() - - 同 Length - 数组长度

一个细节证明 FreeSql 匠心制作

通用的 in 查询 select.Where(a => new []{ 1,2,3 }.Contains(a.xxx))

假设 xxxs 是 pgsql 的数组字段类型，其实会与上面的 in 查询起冲突，FreeSql 解决了这个矛盾 select.Where(a => a.xxxs.Contains(1))

字典 Dictionary<string, string>

表达式 MySql SqlServer PostgreSQL Oracle 功能说明
a.Count - - case when a is null then 0 else array_length(akeys(a),1) end - 字典长度
a.Keys - - akeys(a) - 返回字典所有key数组
a.Values - - avals(a) - 返回字典所有value数组
a.Contains(b) - - a @> b - 字典是否包含b
a.ContainsKey(b) - - a? b - 字典是否包含key
a.Concat(b) - - a || b - 字典相连
a.Count() - - 同 Count - 字典长度

JSON JToken/JObject/JArray

表达式 MySql SqlServer PostgreSQL Oracle 功能说明
a.Count - - jsonb_array_length(coalesce(a, '[])) - json数组类型的长度
a.Any() - - jsonb_array_length(coalesce(a, '[])) > 0 - json数组类型，是否为空
a.Contains(b) - - coalesce(a, '{}') @> b::jsonb - json中是否包含b
a.ContainsKey(b) - - coalesce(a, '{}') ? b - json中是否包含键b
a.Concat(b) - - coalesce(a, '{}') b::jsonb
Parse(a) - - a::jsonb - 转化字符串为json类型
a.Field["x"] - - a.Field->x - json成员访问

字符串

表达式 MySql SqlServer PostgreSQL Oracle Sqlite
string.Empty '' '' '' ''
string.IsNullOrEmpty(a) (a is null or a = '') (a is null or a = '') (a is null or a = '') (a is null or a = '') (a is null or a = '')
string.Concat(a,b,c...) concat(a, b, c) a + b + c a || b || c a || b || c a || b || c
a.CompareTo(b) strcmp(a, b) - case when a = b then 0 when a > b then 1 else -1 end case when a = b then 0 when a > b then 1 else -1 end case when a = b then 0 when a > b then 1 else -1 end
a.Contains('b') a like '%b%' a like '%b%' a ilike'%b%' a like '%b%' a like '%b%'
a.EndsWith('b') a like '%b' a like '%b' a ilike'%b' a like '%b' a like '%b'
a.IndexOf(b) locate(a, b) - 1 locate(a, b) - 1 strpos(a, b) - 1 instr(a, b, 1, 1) - 1 instr(a, b) - 1
a.Length char_length(a) len(a) char_length(a) length(a) length(a)
a.PadLeft(b, c) lpad(a, b, c) - lpad(a, b, c) lpad(a, b, c) lpad(a, b, c)
a.PadRight(b, c) rpad(a, b, c) - rpad(a, b, c) rpad(a, b, c) rpad(a, b, c)
a.Replace(b, c) replace(a, b, c) replace(a, b, c) replace(a, b, c) replace(a, b, c) replace(a, b, c)
a.StartsWith('b') a like 'b%' a like 'b%' a ilike'b%' a like 'b%' a like 'b%'
a.Substring(b, c) substr(a, b, c + 1) substring(a, b, c + 1) substr(a, b, c + 1) substr(a, b, c + 1) substr(a, b, c + 1)
a.ToLower lower(a) lower(a) lower(a) lower(a) lower(a)
a.ToUpper upper(a) upper(a) upper(a) upper(a) upper(a)
a.Trim trim(a) trim(a) trim(a) trim(a) trim(a)
a.TrimEnd rtrim(a) rtrim(a) rtrim(a) rtrim(a) rtrim(a)
a.TrimStart ltrim(a) ltrim(a) ltrim(a) ltrim(a) ltrim(a)
a.FirstOrDefault substr(a,1,1) substring(a,1,1) substr(a,1,1) substr(a,1,1) substr(a,1,1)

使用字符串函数可能会出现性能瓶颈，虽然不推荐使用，但是作为功能库这也是不可缺少的功能之一。

日期

表达式 MySql SqlServer PostgreSQL Oracle
DateTime.Now now() getdate() current_timestamp systimestamp
DateTime.UtcNow utc_timestamp() getutcdate() (current_timestamp at time zone 'UTC') sys_extract_utc(systimestamp)
DateTime.Today curdate convert(char(10),getdate(),120) current_date trunc(systimestamp)
DateTime.MaxValue cast('9999/12/31 23:59:59' as datetime) '9999/12/31 23:59:59' '9999/12/31 23:59:59'::timestamp to_timestamp('9999-12-31 23:59:59','YYYY-MM-DD HH24:MI:SS.FF6')
DateTime.MinValue cast('0001/1/1 0:00:00' as datetime) '1753/1/1 0:00:00' '0001/1/1 0:00:00'::timestamp to_timestamp('0001-01-01 00:00:00','YYYY-MM-DD HH24:MI:SS.FF6')
DateTime.Compare(a, b) a - b a - b extract(epoch from a::timestamp-b::timestamp) extract(day from (a-b))
DateTime.DaysInMonth(a, b) dayofmonth(last_day(concat(a, '-', b, '-1'))) datepart(day, dateadd(day, -1, dateadd(month, 1, cast(a as varchar) + '-' + cast(b as varchar) + '-1'))) extract(day from (a
DateTime.Equals(a, b) a = b a = b a = b a = b
DateTime.IsLeapYear(a) a%4=0 and a%100<>0 or a%400=0 a%4=0 and a%100<>0 or a%400=0 a%4=0 and a%100<>0 or a%400=0 mod(a,4)=0 AND mod(a,100)<>0 OR mod(a,400)=0
DateTime.Parse(a) cast(a as datetime) cast(a as datetime) a::timestamp to_timestamp(a,'YYYY-MM-DD HH24:MI:SS.FF6')
a.AddDays(b) date_add(a, interval b day) dateadd(day, b, a) a::timestamp+(b
a.AddHours(b) date_add(a, interval b hour) dateadd(hour, b, a) a::timestamp+(b
a.AddMilliseconds(b) date_add(a, interval b*1000 microsecond) dateadd(millisecond, b, a) a::timestamp+(b
a.AddMinutes(b) date_add(a, interval b minute) dateadd(minute, b, a) a::timestamp+(b
a.AddMonths(b) date_add(a, interval b month) dateadd(month, b, a) a::timestamp+(b
a.AddSeconds(b) date_add(a, interval b second) dateadd(second, b, a) a::timestamp+(b
a.AddTicks(b) date_add(a, interval b/10 microsecond) dateadd(millisecond, b / 10000, a) a::timestamp+(b
a.AddYears(b) date_add(a, interval b year) dateadd(year, b, a) a::timestamp+(b
a.Date cast(date_format(a, '%Y-%m-%d') as datetime) convert(char(10),a,120) a::date trunc(a)
a.Day dayofmonth(a) datepart(day, a) extract(day from a::timestamp) cast(to_char(a,'DD') as number)
a.DayOfWeek dayofweek(a) datepart(weekday, a) - 1 extract(dow from a::timestamp) case when to_char(a)='7' then 0 else cast(to_char(a) as number) end
a.DayOfYear dayofyear(a) datepart(dayofyear, a) extract(doy from a::timestamp) cast(to_char(a,'DDD') as number)
a.Hour hour(a) datepart(hour, a) extract(hour from a::timestamp) cast(to_char(a,'HH24') as number)
a.Millisecond floor(microsecond(a) / 1000) datepart(millisecond, a) extract(milliseconds from a::timestamp)-extract(second from a::timestamp)*1000 cast(to_char(a,'FF3') as number)
a.Minute minute(a) datepart(minute, a) extract(minute from a::timestamp) cast(to_char(a,'MI') as number)
a.Month month(a) datepart(month, a) extract(month from a::timestamp) cast(to_char(a,'FF3') as number)
a.Second second(a) datepart(second, a) extract(second from a::timestamp) cast(to_char(a,'SS') as number)
a.Subtract(b) timestampdiff(microsecond, b, a) datediff(millisecond, b, a) * 1000 (extract(epoch from a::timestamp-b::timestamp)*1000000) a - b
a.Ticks timestampdiff(microsecond, '0001-1-1', a) * 10 datediff(millisecond, '1970-1-1', a) * 10000 + 621355968000000000 extract(epoch from a::timestamp)*10000000+621355968000000000 cast(to_char(a,'FF7') as number)
a.TimeOfDay timestampdiff(microsecond, date_format(a, '%Y-%m-%d'), a) '1970-1-1 ' + convert(varchar, a, 14) extract(epoch from a::time)*1000000 a - trunc(a)
a.Year year(a) datepart(year, a) extract(year from a::timestamp) 年
a.Equals(b) a = b a = b a = b a = b
a.CompareTo(b) a - b a - b a - b a - b
a.ToString() date_format(a, '%Y-%m-%d %H:%i:%s.%f') convert(varchar, a, 121) to_char(a, 'YYYY-MM-DD HH24:MI:SS.US') to_char(a,'YYYY-MM-DD HH24:MI:SS.FF6')

数学函数

表达式 MySql SqlServer PostgreSQL Oracle
Math.Abs(a) abs(a) abs(a) abs(a)
Math.Acos(a) acos(a) acos(a) acos(a) acos(a)
Math.Asin(a) asin(a) asin(a) asin(a) asin(a)
Math.Atan(a) atan(a) atan(a) atan(a) atan(a)
Math.Atan2(a, b) atan2(a, b) atan2(a, b) atan2(a, b) -
Math.Ceiling(a) ceiling(a) ceiling(a) ceiling(a) ceil(a)
Math.Cos(a) cos(a) cos(a) cos(a) cos(a)
Math.Exp(a) exp(a) exp(a) exp(a) exp(a)
Math.Floor(a) floor(a) floor(a) floor(a) floor(a)
Math.Log(a) log(a) log(a) log(a) log(e,a)
Math.Log10(a) log10(a) log10(a) log10(a) log(10,a)
Math.PI(a) 3.1415926535897931 3.1415926535897931 3.1415926535897931 3.1415926535897931
Math.Pow(a, b) pow(a, b) power(a, b) pow(a, b) power(a, b)
Math.Round(a, b) round(a, b) round(a, b) round(a, b) round(a, b)
Math.Sign(a) sign(a) sign(a) sign(a) sign(a)
Math.Sin(a) sin(a) sin(a) sin(a) sin(a)
Math.Sqrt(a) sqrt(a) sqrt(a) sqrt(a) sqrt(a)
Math.Tan(a) tan(a) tan(a) tan(a) tan(a)
Math.Truncate(a) truncate(a, 0) floor(a) trunc(a, 0) trunc(a, 0)

类型转换

表达式 MySql SqlServer PostgreSQL Oracle Sqlite
Convert.ToBoolean(a) | bool.Parse(a) a not in ('0','false') a not in ('0','false') a::varchar not in ('0','false','f','no') - a not in ('0','false')
Convert.ToByte(a) | byte.Parse(a) cast(a as unsigned) cast(a as tinyint) a::int2 cast(a as number) cast(a as int2)
Convert.ToChar(a) substr(cast(a as char),1,1) substring(cast(a as nvarchar),1,1) substr(a::char,1,1) substr(to_char(a),1,1) substr(cast(a as character),1,1)
Convert.ToDateTime(a) | DateTime.Parse(a) cast(a as datetime) cast(a as datetime) a::timestamp to_timestamp(a,'YYYY-MM-DD HH24:MI:SS.FF6') datetime(a)
Convert.ToDecimal(a) | decimal.Parse(a) cast(a as decimal(36,18)) cast(a as decimal(36,19)) a::numeric cast(a as number) cast(a as decimal(36,18))
Convert.ToDouble(a) | double.Parse(a) cast(a as decimal(32,16)) cast(a as decimal(32,16)) a::float8 cast(a as number) cast(a as double)
Convert.ToInt16(a) | short.Parse(a) cast(a as signed) cast(a as smallint) a::int2 cast(a as number) cast(a as smallint)
Convert.ToInt32(a) | int.Parse(a) cast(a as signed) cast(a as int) a::int4 cast(a as number) cast(a as smallint)
Convert.ToInt64(a) | long.Parse(a) cast(a as signed) cast(a as bigint) a::int8 cast(a as number) cast(a as smallint)
Convert.ToSByte(a) | sbyte.Parse(a) cast(a as signed) cast(a as tinyint) a::int2 cast(a as number) cast(a as smallint)
Convert.ToSingle(a) | float.Parse(a) cast(a as decimal(14,7)) cast(a as decimal(14,7)) a::float4 cast(a as number) cast(a as float)
Convert.ToString(a) cast(a as char) cast(a as nvarchar) a::varchar to_char(a) cast(a as character)
Convert.ToUInt16(a) | ushort.Parse(a) cast(a as unsigned) cast(a as smallint) a::int2 cast(a as number) cast(a as unsigned)
Convert.ToUInt32(a) | uint.Parse(a) cast(a as unsigned) cast(a as int) a::int4 cast(a as number) cast(a as decimal(10,0))
Convert.ToUInt64(a) | ulong.Parse(a) cast(a as unsigned) cast(a as bigint) a::int8 cast(a as number) cast(a as decimal(21,0))
Guid.Parse(a) substr(cast(a as char),1,36) cast(a as uniqueidentifier) a::uuid substr(to_char(a),1,36) substr(cast(a as character),1,36)
Guid.NewGuid() - newid() - - -
new Random().NextDouble() rand() rand() random() dbms_random.value random()

参考资料

Basic

使用指南

学习与交流

信息

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