Oh, thank for you excellent explain, i almost thought i found a bug!
在2021年11月11日星期四 UTC+8 下午2:18:00<Jeremy Evans> 写道：
> On Wed, Nov 10, 2021 at 7:14 AM Billy Zheng <vil...@gmail.com> wrote:
>
>> Please see a example.
>>
>> I have a table, name institutions, and exists a :name column.
>>
>> Following is SQL generate by Sequel, please notice, there is a alias like
>> this:
>>
>> stock"."name" AS "stock_name"
>>
>
> This is expected. Without this alias, the identifier symbol used for the
> returned column would be "name", which would clash with the "name" from
> "institutions"."name". Sequel's graphing code always tries to generate
> unique aliases.
>
>
>> ```
>> SELECT "institutions"."id", "institutions"."name",
>> "institutions"."number_of_holding", "instit
>> utions"."market_value", "institutions"."percent_of_shares_for_stock",
>> "institutions"."percent_
>> of_shares_for_institution", "institutions"."quarterly_changes_percent",
>> "institutions"."quarte
>> rly_changes", "institutions"."market_value_dollar_string",
>> "institutions"."holding_cost", "ins
>> titutions"."date", "institutions"."created_at",
>> "institutions"."stock_id", "institutions"."fir
>> m_id", "stock"."id" AS "stock_id_0", "stock"."name" AS "stock_name",
>> "stock"."exchange_id", "s
>> tock"."percent_of_institutions", "stock"."ipo_price",
>> "stock"."ipo_amount", "stock"."ipo_place
>> ment", "stock"."ipo_date", "stock"."ipo_average_price",
>> "stock"."ipo_placement_number", "stock
>> "."next_earnings_date", "exchange"."id" AS "exchange_id_0",
>> "exchange"."name" AS "exchange_nam
>> e", "firm"."id" AS "firm_id_0", "firm"."name" AS "firm_name",
>> "firm"."display_name" FROM "inst
>> itutions" LEFT OUTER JOIN "stocks" AS "stock" ON ("stock"."id" =
>> "institutions"."stock_id") LE
>> FT OUTER JOIN "exchanges" AS "exchange" ON ("exchange"."id" =
>> "stock"."exchange_id") LEFT OUTE
>> R JOIN "firms" AS "firm" ON ("firm"."id" = "institutions"."firm_id")
>> ORDER BY "stock"."name"
>> ```
>>
>> Then i remove :name column use sequel migration, then run same code, get
>> following new SQL.
>>
>
> In this query, there is no "institutions"."name", so there is no reason to
> alias "stock"."name" in order to disambiguate.
>
>
>>
>> SELECT "institutions"."id", "institutions"."number_of_holding",
>> "institutions"."market_value",
>> "institutions"."percent_of_shares_for_stock",
>> "institutions"."percent_of_shares_for_instituti
>> on", "institutions"."quarterly_changes_percent",
>> "institutions"."quarterly_changes", "institut
>> ions"."market_value_dollar_string", "institutions"."holding_cost",
>> "institutions"."date", "ins
>> titutions"."created_at", "institutions"."stock_id",
>> "institutions"."firm_id", "stock"."id" AS
>> "stock_id_0", "stock"."name", "stock"."exchange_id",
>> "stock"."percent_of_institutions", "stock
>> "."ipo_price", "stock"."ipo_amount", "stock"."ipo_placement",
>> "stock"."ipo_date", "stock"."ipo
>> _average_price", "stock"."ipo_placement_number",
>> "stock"."next_earnings_date", "exchange"."id"
>> AS "exchange_id_0", "exchange"."name" AS "exchange_name", "firm"."id" AS
>> "firm_id_0", "firm".
>> "name" AS "firm_name", "firm"."display_name" FROM "institutions" LEFT
>> OUTER JOIN "stocks" AS "
>> stock" ON ("stock"."id" = "institutions"."stock_id") LEFT OUTER JOIN
>> "exchanges" AS "exchange"
>> ON ("exchange"."id" = "stock"."exchange_id") LEFT OUTER JOIN "firms" AS
>> "firm" ON ("firm"."id
>> " = "institutions"."firm_id") ORDER BY "stock"."name"
>>
>> The strange things is, why the first SQL generate stock"."name" AS
>> "stock_name", and the second SQL not create alias like "AS "stock_name" ?
>>
>
> It's needed for disambiguation in the first case, but not in the second
> case.
>
> Thanks,
> Jeremy
>
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