我正在编写一个查询 SQL 数据库的函数,我遇到了一个让我难过的 ReadOnlyMemoryError()。问题是,当我将代码作为简单脚本运行时,一切都按预期运行。但是,当我尝试将完全相同的代码包装在一个函数中时,我得到了 ReadOnlyMemoryError()。
这是我的代码的脚本版本:
using ODBC
using DBInterface
using Dates
using DataFrames
server = "server string "
username = "username "
password = " password"
db = " db name"
start_date=Nothing
end_date=Nothing
if start_date == Nothing || typeof(start_date) != "Date"
start_date = Dates.today() - Dates.Day(30)
end
if end_date == Nothing || typeof(end_date) != "Date"
end_date = Dates.today()
end
query = """ SQL SELECT statement """
connect_string = "DRIVER={ODBC Driver 17 for SQL Server};SERVER=" * server *
";DATABASE=" * db *
";UID=" * username *
";PWD=" * password
conn = ODBC.Connection(connect_string)
df = DBInterface.execute(conn, query) |> DataFrame
这按预期工作,结果是一个包含大约 50 万行的数据框 df。但是,当我尝试使用相同的代码来制作可重用函数时,出现错误:
using ODBC
using DBInterface
using Dates
using DataFrames
function get_cf_data(start_date=Nothing, end_date=Nothing)
server = " server string "
username = " user name"
password = " password"
db = " db "
if start_date == Nothing || typeof(start_date) != "Date"
start_date = Dates.today() - Dates.Day(30)
end
if end_date == Nothing || typeof(end_date) != "Date"
end_date = Dates.today()
end
query = """ SQL SELECT statement """
connect_string = "DRIVER={ODBC Driver 17 for SQL Server};SERVER=" * server *
";DATABASE=" * db *
";UID=" * username *
";PWD=" * password
conn = ODBC.Connection(connect_string)
df = DBInterface.execute(conn, query) |> DataFrame
return df
end
在这种情况下,当我尝试从 REPL get_cf_data() 调用时,我得到错误:ReadOnlyMemoryError()。我对 Julia 有点陌生,所以任何见解都将不胜感激。谢谢!
最佳答案
如评论所述,大多数编程语言在集成 ODBC 连接等 API 时的最佳做法是在使用后关闭并释放其资源。
此外,请考虑 parameterization (运行传递文字值的 SQL 的任何语言的最佳实践)您在其中设置准备好的 SQL 语句并在后续的 execute
调用中绑定(bind)值。
function get_cf_data(start_date=Nothing, end_date=Nothing)
server = " server string "
username = " user name"
password = " password"
db = " db "
if isnothing(start_date) || typeof(start_date) != "Date"
start_date = Dates.today() - Dates.Day(30)
end
if isnothing(end_date) || typeof(end_date) != "Date"
end_date = Dates.today()
end
# PREPARED STATEMENT WITH QMARK PLACEHOLDERS
sql = """SELECT Col1, Col2, Col3, ...
FROM myTable
WHERE myDate BETWEEN ? AND ?
"""
connect_string = "DRIVER={ODBC Driver 17 for SQL Server};SERVER=" * server *
";DATABASE=" * db *
";UID=" * username *
";PWD=" * password
conn = ODBC.Connection(connect_string)
# PREPARE STATEMENT AND BIND PARAMS
stmt = DBInterface.prepare(conn, sql)
df = DBInterface.execute(stmt, (start_date, end_date)) |> DataFrame
DBInterface.close(stmt) # CLOSE STATEMENT
DBInterface.close(conn) # CLOSE CONNECTION
stmt = Nothing; conn = Nothing # UNINTIALIZE OBJECTS
return df
end
关于sql - 带有 ODBC SQL 查询的 Julia ReadOnlyMemoryError,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/64755530/