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→Finding Companies that Underwent IPOs and MAs
#LEFT JOIN the MA table with the IPO table. Join on primary keys of portcos. Select the companies where the IPO table are null as these are the companies that only had MAs. Do the same for IPOs. Now you have tables of companies that underwent only MAs and only IPOs.
#Join the companies that underwent IPOs only and the chosen IPOs back to the original key using the primary key of the company which must be in both tables. Repeat this for the MA table.
===Ed's version===
Note: your version isn't wrong. I'm just trying to be clearer.
==Finding Companies that Underwent IPOs and MAs==
#Load IPOClean and MAClean into the database.
#Make a table of keys by doing a JOIN on the two tables in order to find the companies that underwent both MAs and IPOs. (Do this by joining on the primary keys of portcos in both tables.) Make another table by left joining these results back with IPOClean and MAClean. COPY this table into an excel sheet and manually find which companies you want to keep as MAs and which you want to keep as IPOs. Make sure to keep the portco primary key in this table.
#Load the decided IPO and MA data back into the database into a table called IPOMASelected, including the primary keys of the portcos, and the primary keys of the MAs and IPOs selected.
#Make a table of primary keys of portcos and MAs and IPOs called ExitKeysClean. Do this by taking the IPOs which didn't have MAs from IPOClean and the MAs which didn't have IPOs from MAClean and the selected MAs and IPOs from IPOMASelected. Note that one way to do this is to LEFT JOIN the MA table with the IPO table. Select the companies where the IPO table are null as these are the companies that only had MAs. Do the same for IPOs. Now you have tables of companies that underwent only MAs and only IPOs.
#Make a table called PortCoExits by compiling information from ExitKeysClean Left joined to your main (no duplicates) IPO and MA tables, and using CASE WHEN statements.
Example Join on a composite Key:
DROP TABLE IPOMAForReview;
CREATE TABLE IPOMAForReview
SELECT A.*, B.targetname, B.targetstate, B.announcedate
FROM IPOClean AS A
JOIN MAClean AS B ON A.coname=B.coname AND A.statecode=B.statecode AND A.datefirstinv=B.datefirstinv;
Example CASE WHEN statement:
DROP TABLE PortCoExits;
CREATE TABLE PortCoExits
SELECT A.coname, A.statecode, A.datefirst,
CASE WHEN b.coname IS NOT NULL THEN 1::int WHEN c.coname IS NOT NULL THEN 0::int ELSE NULL::int END AS IPOvsMA,
CASE WHEN b.coname IS NOT NULL THEN b.proceedsall WHEN c.coname IS NOT NULL THEN c.transactionvalue ELSE NULL::int END AS exitvalue,
...
FROM ExitKeysClean AS A
LEFT JOIN IPONoDups AS B ON A.issuername=B.issuername AND A.statecode=B.statecode AND A.issuedate=B.issuedate
LEFT JOIN MANoDups AS B ON A.targetname=B.targetname AND A.statecode=B.statecode AND A.announcedate=B.announcedate;
When putting values together, make sure that they are in the same units (pref $m).
