如何在postgresql group by子句中为分组行添加数字

Question

我有一个PostgreSQL表，在文本列中包含重复值。它看起来像这样：

/usr/local/bin/python
# -*- coding: utf-8 -*-
import sys
from PyQt4 import QtCore, QtGui

try:
    _fromUtf8 = QtCore.QString.fromUtf8
except AttributeError:
    def _fromUtf8(s):
        return s

try:
    _encoding = QtGui.QApplication.UnicodeUTF8

    def _translate(context, text, disambig):
        return QtGui.QApplication.translate(context, text, disambig, _encoding)
except AttributeError:
    def _translate(context, text, disambig):
        return QtGui.QApplication.translate(context, text, disambig)


class Ui_MainWindow(object):
    def setupUi(self, MainWindow):
        MainWindow.setObjectName(_fromUtf8("MainWindow"))
        MainWindow.resize(845, 620)
        self.centralwidget = QtGui.QWidget(MainWindow)
        self.centralwidget.setObjectName(_fromUtf8("centralwidget"))
        self.gridLayout = QtGui.QGridLayout(self.centralwidget)
        self.gridLayout.setObjectName(_fromUtf8("gridLayout"))
        self.pushButton_2 = QtGui.QPushButton(self.centralwidget)
        font = QtGui.QFont()
        font.setFamily(_fromUtf8("Times New Roman"))
        font.setPointSize(24)
        font.setBold(True)
        font.setWeight(75)
        self.pushButton_2.setFont(font)
        self.pushButton_2.setObjectName(_fromUtf8("pushButton_2"))
        self.gridLayout.addWidget(self.pushButton_2, 1, 1, 1, 1)
        self.pushButton_3 = QtGui.QPushButton(self.centralwidget)
        font = QtGui.QFont()
        font.setFamily(_fromUtf8("Times New Roman"))
        font.setPointSize(24)
        font.setBold(True)
        font.setWeight(75)
        self.pushButton_3.setFont(font)
        self.pushButton_3.setObjectName(_fromUtf8("pushButton_3"))
        self.gridLayout.addWidget(self.pushButton_3, 1, 2, 1, 1)
        self.pushButton = QtGui.QPushButton(self.centralwidget)
        font = QtGui.QFont()
        font.setFamily(_fromUtf8("Times New Roman"))
        font.setPointSize(24)
        font.setBold(True)
        font.setWeight(75)
        self.pushButton.setFont(font)
        self.pushButton.setObjectName(_fromUtf8("pushButton"))
        self.gridLayout.addWidget(self.pushButton, 1, 0, 1, 1)
        self.label = QtGui.QLabel(self.centralwidget)
        font = QtGui.QFont()
        font.setPointSize(48)
        font.setBold(True)
        font.setItalic(False)
        font.setWeight(75)
        self.label.setFont(font)
        self.label.setObjectName(_fromUtf8("label"))
        self.gridLayout.addWidget(self.label, 0, 1, 1, 1)
        self.label_2 = QtGui.QLabel(self.centralwidget)
        font = QtGui.QFont()
        font.setPointSize(36)
        font.setBold(True)
        font.setWeight(75)
        self.label_2.setFont(font)
        self.label_2.setObjectName(_fromUtf8("label_2"))
        self.gridLayout.addWidget(self.label_2, 2, 1, 1, 1)
        MainWindow.setCentralWidget(self.centralwidget)
        self.menubar = QtGui.QMenuBar(MainWindow)
        self.menubar.setGeometry(QtCore.QRect(0, 0, 845, 21))
        self.menubar.setObjectName(_fromUtf8("menubar"))
        MainWindow.setMenuBar(self.menubar)
        self.statusbar = QtGui.QStatusBar(MainWindow)
        self.statusbar.setObjectName(_fromUtf8("statusbar"))
        MainWindow.setStatusBar(self.statusbar)

        self.retranslateUi(MainWindow)
        QtCore.QMetaObject.connectSlotsByName(MainWindow)

    def retranslateUi(self, MainWindow):
        MainWindow.setWindowTitle(_translate("MainWindow", "MainWindow", None))
        self.pushButton_2.setText(_translate("MainWindow", "Ordrebekræftelse", None))
        self.pushButton_3.setText(_translate("MainWindow", "Tilbud", None))
        self.pushButton.setText(_translate("MainWindow", " Faktura", None))
        self.label.setText(_translate("MainWindow", "Aaskov Gardiner", None))
        self.label_2.setText(_translate("MainWindow", "  v/ Bent H. Troelsen", None))

我需要为组中的每个值添加一个包含不同数字的列，因此我的表应如下所示：

gid, capt
1, foo
2, foo
3, bar
4, bar
5, bar
6, buz
7, buz

它是每个组内的一种行号，始终从1开始。任何人都可以向我提供适当的SELECT语句吗？

Answer 1

在this question and its answers的帮助下：

SELECT gid, capt, row_number() OVER (PARTITION BY capt ORDER BY gid) AS rnum
FROM your_table_here ORDER BY gid;

row_number window function提供了计数。

PARTITION BY子句中的OVER语句告诉数据库重新编号，每次更改为capt。 ORDER BY子句中的OVER告诉数据库与gid列一起计数。

Answer 2

可以使用window functions：

完成此操作

select gid, 
       capt, 
       row_number() over (partition by capt order by gid) as rnum
from the_table
order by capt, gid;