基于postgreSql 常用查询小结

1. 日期格式转化（参考）

select beg_time, end_time, extract(epoch from to_timestamp(end_time,'yyyy-mm-dd-HH24-MI-SS-US'))-extract(epoch from to_timestamp(beg_time,'yyyy-mm-dd-HH24-MI-SS-US')) from cdb_all_iu_data where beg_time > '2017-09-21' 

注：beg_time, end_time以TEXT形式存储，求时间差时转化为时间戳再相减得到结果（s）

2. select * from (中间结果) t

select count(*) from (
select chkid, count(*) from abc_table GROUP BY chkid) t

补充：自己写的postgreSQL查询语句

我就废话不多说了，大家还是直接看代码吧~

import psycopg2
class PostgreConn():
  '''
  数据库连接类
  '''
  def __init__(self, database, user, password, host, port):
    self.conn = psycopg2.connect(database=database, user=user, password=password, host=host, port=port)
    print('数据库连接成功')
    self.cur = self.conn.cursor()
    self.rows = None

  def cur(self):
    return self.cur()

  def execute(self, sql, fetchone=0):
    self.cur.execute(sql)
    if fetchone:
      self.rows = self.cur.fetchone()
    else:
      self.rows = self.cur.fetchall()
    return self.rows

  def close(self):
    self.cur.close()
    self.conn.close()
    print('数据库连接关闭') 

def select_sql(table, keys, conditions, isdistinct=0):
  '''
    生成select的sql语句
  @table，查询记录的表名
  @key，需要查询的字段
  @conditions,插入的数据，字典
  @isdistinct,查询的数据是否不重复
  '''
  if isdistinct:
    sql = 'SELECT distinct %s ' % ",".join(keys)
  else:
    sql = 'SELECT %s ' % ",".join(keys)
  sql += ' from %s ' % table
  if conditions:
    sql += ' WHERE %s ' % dict_str_and(conditions)
  return sql 

def dict_str_and(dictin):
  '''
  将字典变成，key='value' and key='value'的形式
  '''
  tmplist = []
  for k, v in dictin.items():
    tmp = "%s='%s'" % (str(k), str(v))
    tmplist.append(' ' + tmp + ' ')
  return ' and '.join(tmplist) 

def fSqlResult(r,key_list):
  '''
  :param r: 数据库fetchall的结果
  :param key_list: 查询字段的keys
  :return:
  format SQL Result 格式化数据库查询的结果，转化成包含多个字典的列表格式，即((1,2),(3,4))->[{"key1":1,"key2":2},{"key1":3,"key2":4}]
  返回 @dict 查询结果
  '''
  mlist=[]
  l=len(key_list)
  if r:
    for item in r:
      tmp={}
      for i in range(l):
        tmp[key_list[i]]=str(item[i])
      mlist.append(tmp)
  return mlist 

conn = PostgreConn('settle', 'admin', 'settle8', '123.57.285.89', '5432')
key_list = ['user_id']
sql = select_sql('st_user', key_list, {'phone': '138****'})
print(sql)
r = conn.execute(sql)
re = fSqlResult(r, key_list)
print(re)
conn.close()

以上为个人经验，希望能给大家一个参考，也希望大家多多支持我们。如有错误或未考虑完全的地方，望不吝赐教。